Split prism illuminator for spatial light modulator

ABSTRACT

An optical device includes a first polarization selective reflector positioned in a first orientation so that the first polarization selective reflector: receives first light in a first direction; redirects a first portion, of the first light, having a first polarization to a second direction that is non-parallel to the first direction; and receives second light in a third direction and transmit a first portion, of the second light. A second polarization selective reflector positioned in a second orientation non-parallel to the first orientation, and adjacent to the first polarization selective reflector so that the second polarization selective reflector: receives third light in a fourth direction; redirects a first portion, of the third light, having the first polarization to a fifth direction that is non-parallel to the fourth direction; and receives fourth light in a sixth direction and transmit a first portion, of the fourth light having the second polarization.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/850,473, filed May 20, 2019, which is incorporated by referenceherein in its entirety. This application is related to U.S. patentapplication Ser. No. 16/874,115, entitled “Compact Spatial LightModulator Projection System,” filed on May 14, 2020, U.S. patentapplication Ser. No. 16/874,259, entitled “Compact Spatial LightModulator Illumination System,” filed on May 14, 2020, U.S. patentapplication Ser. No. 16/874,134, entitled “Polarization Sensitive BeamSplitter,” filed on May 14, 2020, and U.S. patent application Ser. No.16/874,265, entitled “Polarizing Beam Splitter Assembly,” filed on May14, 2020. All of these applications are incorporated by reference hereinin their entireties.

TECHNICAL FIELD

This relates generally to head-mounted display devices, and morespecifically to optical components used in head-mounted display devices.

BACKGROUND

Head-mounted display devices (also called herein head-mounted displays)are gaining popularity as means for providing visual information tousers.

However, the size and weight of conventional head-mounted display devicehave limited application of head-mounted display devices.

SUMMARY

Accordingly, there is a need for head-mounted display devices that aremore compact and lightweight. Compact head-mounted display devices wouldalso improve user satisfaction with such devices.

The deficiencies and other problems are reduced or eliminated by thedisclosed devices, systems, and methods.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned in a first orientation sothat the first polarization selective reflector receives first light ina first direction, redirects a first portion, of the first light, havinga first polarization to a second direction that is non-parallel to thefirst direction; and receives second light in a third direction andtransmit a first portion, of the second light, having a secondpolarization orthogonal to the first polarization. The optical deviceincludes a second polarization selective reflector positioned in asecond orientation non-parallel to the first orientation, and adjacentto the first polarization selective reflector so that the secondpolarization selective reflector receives third light in a fourthdirection; redirects a first portion, of the third light, having thefirst polarization to a fifth direction that is non-parallel to thefourth direction; and receives fourth light in a sixth direction andtransmit a first portion, of the fourth light having the secondpolarization.

In some embodiments, the second direction is orthogonal to the firstdirection and the fifth direction is orthogonal to the third direction.

In some embodiments, the first polarization selective reflector isfurther configured to transmit a second portion, of the first light,having the second polarization; and the second polarization selectivereflector is further configured to receive, and transmit, the secondportion, of the first light having the second polarization.

In some embodiments, the optical device further includes a thirdreflector configured to receive from the second polarization selectivereflector the second portion of the first light, and redirect the secondportion of the first light back to the second polarization selectivereflector as the second light.

In some embodiments, the optical device further includes a light sourceconfigured to output the first light having the first polarization.

In some embodiments, the optical device further includes an opticalintegrator configured receive the first light and redirect the firstlight such that the first light transmitted by the optical integratorhas a smaller divergence than the first light incident on the opticalintegrator. In some embodiments, the optical device further includes aFresnel reflector optically coupled with the first polarizationselective reflector, the Fresnel reflector configured to receive thefirst light output by the light source and redirect the first lighttoward the first polarization selective reflector. In some embodiments,the Fresnel reflector is configured to expand a beam size of the firstlight.

In some embodiments, the optical device further includes a waveplatedisposed between the third reflector and the second polarizationselective reflector. In some embodiments, the waveplate is configured toconvert linearly polarized light to circularly polarized light and toconvert circularly polarized light to linearly polarized light (e.g., aquarter-wave plate).

In some embodiments, the first polarization selective reflector isfurther configured to reflect a second portion, of the second light,having the first polarization in a seventh direction distinct from thethird direction; and the second polarization selective reflector isfurther configured to reflect a second portion, of the fourth light,having the first polarization, in an eighth direction distinct from thesixth direction.

In some embodiments, the optical device further includes a reflectivespatial light modulator optically coupled with the first polarizationselective reflector and the second polarization selective reflector, thereflective spatial light modulator configured to: receive, on a firstregion of the reflective spatial light modulator, the first portion ofthe first light having the first polarization and reflect the firstportion of the first light as the second light. The reflective spatiallight modulator is also configured to receive, on a second regionadjacent to the first region of the reflective spatial light modulator,the first portion of the third light having the first polarization andreflect the first portion of the third light as the fourth light.

In some embodiments, the reflective spatial light modulator includes areflective surface and a plurality of pixels, a respective pixel in theplurality of pixels having respective modulating elements. In someembodiments, reflecting the first portion of the first light as thesecond light and reflecting the first portion of the third light as thefourth light includes modulating, by the respective modulating elements,polarization of the first portion of the first light and the firstportion of the third light.

In some embodiments, the reflective spatial light modulator is a LiquidCrystal on Silicon (LCoS) display.

In some embodiments, the first polarization selective reflector in thefirst orientation and the second polarization selective reflector in thesecond orientation define an angle that is approximately 90 degrees. Insome embodiments, the angle is more or less than 90 degrees. The firstpolarization selective reflector and the second polarization selectivereflector are coupled to each other.

In some embodiments, the optical device further includes a prismdefining a first facet and a second facet. The first polarizationselective reflector is disposed on the first facet and the secondpolarization selective reflector is disposed on the second facet. Insome embodiments, the first polarization selective reflector and thesecond polarization selective reflector are selected from the groupconsisting of: a wire grid polarizer, a birefringent optical filmreflective polarizer, a cholesteric reflective polarizer, and aMacNeille polarizer.

In some embodiments, the optical device further includes a first lightsource configured to output the first light having the firstpolarization; and a second light source configured to output the thirdlight having the first polarization.

In some embodiments, the optical device further includes a first Fresnelreflector optically coupled with the first polarization selectivereflector configured to receive the first light output by the firstlight source; and redirect the first light toward the first polarizationselective reflector in the first direction. The optical device furtherincludes a second Fresnel reflector optically coupled with the secondpolarization selective reflector configured to receive the third lightoutput by the second light source and redirect the third light towardthe second polarization selective reflector in the fourth direction.

In some embodiments, the fourth direction is substantially parallel tothe first direction. In some embodiments, the fifth direction issubstantially parallel to the second direction. In some embodiments, thefifth direction is non-parallel to the second direction.

In accordance with some embodiments, a method includes, with a firstpolarization selective reflector positioned in a first orientation,receiving first light in a first direction; redirecting a first portion,of the first light, having a first polarization to a second directionthat is non-parallel to the first direction. The method includesreceiving second light in a third direction, transmit a first portion,of the second light having a second polarization orthogonal to the firstpolarization. The method also includes, with a second polarizationselective reflector positioned in a second orientation non-parallel tothe first orientation, and adjacent to the first polarization selectivereflector, receiving third light in a fourth direction; redirecting afirst portion, of the third light, having the first polarization to afifth direction that is non-parallel to the fourth direction; andreceiving fourth light in a sixth direction, transmit a first portion,of the fourth light having the second polarization.

In accordance with some embodiments, a method of making an opticalassembly includes placing a first polarization selective reflector in afirst orientation; and placing a second polarization selective reflectorin a second orientation non-parallel, and adjacent, to the firstorientation. In some embodiments, the optical assembly includes apolarization beam splitter.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector, a second polarization selectivereflector; and a third reflector. The first polarization selectivereflector is configured to receive first light and redirect a firstportion, of the first light, having a first polarization and transmit asecond portion, of the first light, having a second polarizationorthogonal to the first polarization. The second polarization selectivereflector is configured to receive from the first polarization selectivereflector, and transmit to the third reflector, the second portion ofthe first light. The third reflector is configured to receive from thesecond polarization selective reflector, and redirect back to the secondpolarization selective reflector, the second portion of the first light;and the second polarization selective reflector is further configured toreceive light from the third reflector and redirect at least a portionof light, the redirected portion having the first polarization.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned relative to a spatial lightmodulator; and a first reflective assembly positioned relative to thefirst polarization selective reflector so that the first polarizationselective reflector receives first light from the spatial lightmodulator and directs at least a portion of the first light having afirst polarization toward the first reflective assembly as second light.The first reflective assembly receives the second light from the firstpolarization selective reflector and directs at least a portion of thesecond light toward the first polarization selective reflector as thirdlight having a second polarization. The second polarization is distinctfrom the first polarization.

In some embodiments, the spatial light modulator is positioned in afirst direction from the first polarization selective reflector, and thefirst reflective assembly is positioned in a second direction from thefirst polarization selective reflector. In some embodiments,illumination light enters the optical device in a third direction fromthe first polarization selective reflector; and a waveguide ispositioned in a fourth direction from the first polarization selectivereflector. The first direction and the second direction are distinctfrom each other.

In some embodiments, the first direction is perpendicular to the thirddirection; and the second direction is perpendicular to the fourthdirection. In some embodiments, the spatial light modulator and thefirst reflective assembly are located in opposite directions from thefirst polarization selective reflector. In some embodiments, the seconddirection is perpendicular to the third direction; and the firstdirection is perpendicular to the fourth direction. In some embodiments,the waveguide and the first reflective assembly are located in oppositedirections from the first polarization selective reflector.

In some embodiments, the optical device further includes a firstreflector. The first reflector defines an opening, and the firstreflector is positioned relative to the spatial light modulator so thatthe spatial light modulator receives light that has (i) passed throughthe opening of the first reflector and (ii) subsequently reflected offthe first reflector. In some embodiments, a second polarizationselective reflector is disposed adjacent to the waveguide. The secondpolarization selective reflector is configured (e.g., by orienting apolarization axis of the second polarization selective reflector) toreflect light having a polarization different (e.g., orthogonal) from apolarization of light reflected by the first polarization selectivereflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to the waveguide. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization identical to apolarization of light reflected by the first polarization selectivereflector.

In some embodiments, a first plane defined by (e.g., containing) thefirst polarization selective reflector intersects a second plane definedby (e.g., containing) the spatial light modulator at a first acuteangle.

In some embodiments, the first reflective assembly includes apolarization retarder and a reflective lens.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by the spatial light modulator has arectangular shape. In some embodiments, a height of the projection isgreater than a width of the projection so that a field of view of thespatial light modulator along the height dimension is larger than afield of view along the width dimension.

In some embodiments, the first polarization selective reflector is atsubstantially 45-degree angle relative to the plane defined by thespatial light modulator. the optical device comprises a first prism anda second prism.

In some embodiments, at least a portion of the first prism has atrapezoidal cross-section having a first edge, a second edge, a thirdedge, a fourth edge. The first edge is perpendicular to the second edge;the second prism is a right-angle prism having a hypotenuse; and thefirst polarization selective reflector is disposed between the firstprism and the second prism, parallel to the hypotenuse of the secondprism and the fourth edge of the first prism. In some embodiments, alength of the hypotenuse is equal to a length of the third edge.

In some embodiments, the first reflective assembly is positionedrelative to the spatial light modulator so that the first polarizationselective reflector directs the second light toward the first reflectiveassembly by transmitting the second light.

In some embodiments, the first reflective assembly is positionedrelative to the spatial light modulator so that the first polarizationselective reflector directs the second light having the firstpolarization toward the first reflective assembly by reflecting thesecond light.

In some embodiments, the first reflective assembly includes a reflectorand a polarization retarder disposed adjacent to the reflector.

In some embodiments, the polarization retarder includes a quarter-waveplate. In some embodiments, the polarization retarder is disposed on afirst surface of a lens and the reflector includes a reflective coatingdisposed on an opposing second surface of the lens.

In accordance to some embodiments, a method includes directing, using afirst polarization selective reflector, first light from a spatial lightmodulator toward a first reflector assembly. The method includesreceiving, using the first reflector assembly, the first light anddirecting at least a portion of the first light toward the firstpolarization selective reflector as second light. The method alsoincludes receiving, using the first polarization selective reflector,the second light and directing at least a portion of the second lighttoward a waveguide (e.g., as third light). The first light has a firstpolarization, and the second light has a second polarization distinctfrom the first polarization (e.g., the second polarization is orthogonalto the first polarization).

In some embodiments, the first polarization selective reflectortransmits the first light toward the first reflector assembly. In someembodiments, the first polarization selective reflector reflects thefirst light toward the first reflector assembly.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector, a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light (e.g., impinging on the first polarization selectivereflector and having a first polarization) toward the secondpolarization selective reflector and the second polarization selectivereflector directs at least a portion of the first light toward the firstpolarization selective reflector as second light. The optical deviceincludes a first reflector positioned relative to the first polarizationselective reflector so that the first polarization selective reflectordirects at least a portion of the second light received from the secondpolarization selective reflector toward the first reflector as thirdlight and the first reflector directs at least a portion of third light(e.g., back) toward the first polarization selective reflector.

In some embodiments, the first reflector is aspherical.

In some embodiments, the first reflector is aspherical to provideuniform illumination at the spatial light modulator.

In some embodiments, the first polarization selective reflector isconfigured to direct the portion of the third light from the firstreflector toward a spatial light modulator. In some embodiments, theoptical device further includes a second reflector positioned relativeto the first polarization selective reflector so that light from thespatial light modulator is directed by the first polarization selectivereflector toward the second reflector and the second reflector directsat least a portion of the light from the spatial light modulator towardsthe first polarization selective reflector. In some embodiments, thesecond reflector projects at least a portion of the light from thespatial light modulator.

In some embodiments, the second polarization selective reflector ispositioned in a first orientation substantially parallel to a plane thatperpendicularly intersects an optical axis of the first reflector. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization different from (e.g.,orthogonal to) a polarization of light reflected by the firstpolarization selective reflector.

In some embodiments, the first polarization selective reflector directsthe first light (having the first polarization) toward the secondpolarization selective reflector by transmitting the first light. Insome embodiments, the second light directed toward the firstpolarization selective reflector by the second polarization selectivereflector is transmitted through the first polarization selectivereflector. In some embodiments, the first polarization selectivereflector directs the portion of the third light from the firstreflector toward a spatial light modulator by reflecting the portion ofthe third light.

In some embodiments, the first polarization selective reflector has afirst surface and an opposing second surface, the first reflector facesthe first surface, and the second polarization selective reflector facesthe second surface.

In some embodiments, the second polarization selective reflector ispositioned in a second orientation substantially orthogonal to a planethat perpendicularly intersects an optical axis of the first reflector.In some embodiments, the second polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the secondpolarization selective reflector) to reflect light having an identicalpolarization as light reflected by the first polarization selectivereflector. In some embodiments, (e.g., FIG. 14E) the first polarizationselective reflector has a first surface and an opposite second surface,both the first reflector and the second polarization selective reflectorface the first surface.

In some embodiments, the first polarization selective reflector directsthe first light (having the first polarization) toward the secondpolarization selective reflector by reflecting the first light towardthe second polarization selective reflector.

In some embodiments, the portion of the second light directed toward thefirst polarization selective reflector by the second polarizationselective reflector is reflected by the first polarization selectivereflector toward the first reflector.

In some embodiments, the first polarization selective reflector directsthe portion of the third light from the first reflector toward thespatial light modulator by transmitting the portion of the third light.

In some embodiments, the first polarization selective reflector has afirst surface and an opposing second surface, and the first surface ofthe first polarization selective reflector faces both the firstreflector and the second polarization selective reflector.

In some embodiments, the first reflector includes structures configuredto scatter the portion of the third light directed toward the firstpolarization selective reflector.

In some embodiments, a first plane defined by (e.g., containing) thefirst polarization selective reflector intersects, at a first acuteangle, with a second plane defined by (e.g., containing) the secondpolarization selective reflector, and intersects, at a second acuteangle, with a third plane defined by (e.g., containing) the firstreflector.

In some embodiments, the optical device further includes a firstpolarization retarder disposed adjacent to the first reflector.

In some embodiments, the first reflector defines a first opening so thatthe first light received by the first polarization selective reflectorhas passed through the first opening.

In some embodiments, an illumination system includes any optical devicedescribed herein, a light source, a homogenizing device configured tocondition light from the light source as output light. The illuminationsystem includes a diverting optic positioned to direct the output lightinto the optical device through the first opening.

In some embodiments, the first polarization retarder defines a secondopening aligned with the first opening of the first reflector.

In accordance to some embodiments, a method includes directing, using afirst polarization selective reflector, first light toward a secondpolarization selective reflector. The method includes receiving, usingthe second polarization selective reflector, the first light anddirecting at least a portion of the first light toward the firstpolarization selective reflector as second light. The method includesreceiving, using the first polarization selective reflector, the secondlight and directing at least a portion of the second light toward afirst reflector as third light. The method also includes receiving,using the first reflector, the third light and directing at least aportion of the third light toward the first polarization selectivereflector as fourth light. The method includes receiving, using thefirst polarization selective reflector, the fourth light and directingat least a portion of the fourth light to illuminate a spatial lightmodulator.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector; a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light having a first nonplanar polarization (e.g., a circularpolarization or an elliptical polarization) toward the secondpolarization selective reflector and the second polarization selectivereflector directs at least a portion of the first light toward the firstpolarization selective reflector as second light. The optical devicealso includes a first reflector positioned relative to the firstpolarization selective reflector so that the first polarizationselective reflector directs at least a portion of the second light(received from the second polarization selective reflector) having asecond nonplanar polarization toward the first reflector as third light.In some embodiments, the first reflector directs at least a portion ofthird light toward the first polarization selective reflector.

In some embodiments, the first polarization selective reflector or thesecond polarization selective reflector is a polarization element thatincludes a metasurface, resonant structures, a chiral layer, or abirefringent material.

In some embodiments, the first reflector directs at least a portion ofthird light having the first nonplanar polarization toward the firstpolarization selective reflector, and the first polarization selectivereflector is configured to direct the portion of the third light fromthe first reflector toward a spatial light modulator as illuminationlight.

In some embodiments, the first polarization selective reflector is aliquid crystal based polarization selective element. In someembodiments, the liquid crystal based polarization selective elementincludes a polarization volume hologram (described with respect to FIGS.16A-16D). In some embodiments, the liquid crystal based polarizationselective element includes cholesteric liquid crystals.

In some embodiments, the optical device further includes a firstreflective assembly positioned relative to the first polarizationselective reflector so that the first polarization selective reflectorreceives first imaging light from a spatial light modulator and directsat least a portion of the first imaging light having a third nonplanarpolarization toward the first reflective assembly as second imaginglight. The first reflective assembly receives the second imaging lightfrom the first polarization selective reflector and directs at least aportion of the second imaging light toward the first polarizationselective reflector as third imaging light having a fourth nonplanarpolarization. The third nonplanar polarization is distinct from thefourth nonplanar polarization.

In some embodiments, the second polarization selective reflector ispositioned in a first orientation that is substantially parallel to aplane that perpendicularly intersects an optical axis of the firstreflector, and the second polarization selective reflector is configured(e.g., by orienting a polarization axis of the second polarizationselective reflector) to reflect light having a polarization differentfrom a polarization of light reflected by the first polarizationselective reflector.

In some embodiments, a first plane defined by the first polarizationselective reflector intersects, at a first acute angle, with a secondplane defined by the second polarization selective reflector, andintersects, at a second acute angle, with a third plane defined by thefirst reflector.

In some embodiments, the first reflector defines a first opening so thatthe first light received by the first polarization selective reflectorhas passed through the first opening.

In some embodiments, an illumination system includes any optical devicedescribed herein, a light source; a homogenizing device configured tocondition light from the light source as output light; and a divertingoptic positioned to direct the output light into the optical devicethrough the first opening.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector positioned relative to a spatial lightmodulator; and a first reflective assembly positioned relative to thefirst polarization selective reflector so that the first polarizationselective reflector receives first light from the spatial lightmodulator and directs at least a portion of the first light having afirst nonplanar polarization toward the first reflective assembly assecond light. The first reflective assembly receives the second lightfrom the first polarization selective reflector and directs at least aportion of the second light having a second nonplanar polarizationtoward the first polarization selective reflector as third light. Thesecond nonplanar polarization is distinct from the first nonplanarpolarization.

In some embodiments, the first polarization selective reflector is apolarization element that includes a metasurface, resonant structures, achiral layer, or a birefringent material.

In some embodiments, the first polarization selective reflector is aliquid crystal based polarization selective element.

In some embodiments, the optical device further includes a firstreflector. In some embodiments, the first reflector defines an opening.The first reflector is positioned relative to the spatial lightmodulator so that the spatial light modulator receives light that has(i) passed through the opening of the first reflector and (ii)subsequently reflected off the first reflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to a waveguide. Thesecond polarization selective reflector is configured to reflect lighthaving a polarization different from a polarization of light reflectedby the first polarization selective reflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to a waveguide. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization identical to apolarization of light reflected by the first polarization selectivereflector.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by the spatial light modulator has arectangular shape.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned in a first orientation sothat the first polarization selective reflector receives first light ina first direction; redirects a first portion, of the first light, havinga first nonplanar polarization to a second direction that isnon-parallel to the first direction. The first polarization selectivereflector receives second light in a third direction and transmit afirst portion, of the second light, having a second nonplanarpolarization orthogonal to the first nonplanar polarization. The opticaldevice includes a second polarization selective reflector positioned ina second orientation non-parallel to the first orientation so that thesecond polarization selective reflector receives third light in a fourthdirection; redirects a first portion, of the third light, having thefirst nonplanar polarization to a fifth direction that is non-parallelto the fourth direction; and receives fourth light in a sixth directionand transmit a first portion, of the fourth light having the secondnonplanar polarization. In some embodiments, the first orientation isadjacent to the first polarization selective reflector.

In some embodiments, the optical device further includes a thirdreflector configured to receive from the second polarization selectivereflector a second portion of the first light transmitted by the firstpolarization selective reflector, and redirect the second portion of thefirst light back to the second polarization selective reflector as thesecond light.

In some embodiments, the optical device further includes a Fresnelreflector optically coupled with the first polarization selectivereflector, the Fresnel reflector configured to receive the first lightoutput by a first light source; and redirect the first light toward thefirst polarization selective reflector.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector; and a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light having a first polarization toward the second polarizationselective reflector and the second polarization selective reflectordirects second light having a second polarization toward the firstpolarization selective reflector. A first plane defined by the firstpolarization selective reflector intersects a second plane defined bythe second polarization selective reflector at a first angle.

In some embodiments, the second light is a portion of the first light.

In some embodiments, the first angle is an acute angle, and the firstangle is measured from a portion of the first plane that directs thefirst light to a portion of the second plane that directs the secondlight.

In some embodiments, the first angle is approximately 45°.

In some embodiments, the optical device further comprises a prismassembly. The first polarization selective reflector is disposed along adiagonal (e.g., an inner diagonal) of the prism assembly. In someembodiments, the diagonal is an inner diagonal of the prism assembly.

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationdifferent from a polarization of light reflected by the secondpolarization selective reflector.

In some embodiments, the optical device further includes a first prism,the second polarization selective reflector is disposed on a firstsurface of the first prism, and light enters the optical device at asecond surface parallel to the first surface.

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationidentical to a polarization of light reflected by the secondpolarization selective reflector.

In some embodiments, the optical device further includes a first prism.The second polarization selective reflector is disposed on a firstsurface of the first prism, and light enters the first prism at a secondsurface perpendicular to the first surface.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by a spatial light modulator isrectangular.

In some embodiments, the first polarization selective reflector ispositioned relative to a spatial light modulator to direct third lighthaving a third polarization, distinct from the first polarization, alonga first direction to the spatial light modulator and the secondpolarization selective reflector is positioned relative to the firstpolarization selective reflector to direct fourth light having the thirdpolarization along the first direction to the spatial light modulator.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by a spatial light modulator has a firstwidth. In some embodiments, a height of the first polarization selectivereflector is larger than the first width, and the height is orthogonalto the first width.

In some embodiments, the first angle is approximately 90 degrees. Insome embodiments, the angle is more or less than 90 degrees.

In some embodiments, the optical device further includes a first prism.The first polarization selective reflector is disposed on a firstsurface of the first prism and the second polarization selectivereflector is disposed on a second surface of the first prism.

In some embodiments, the optical device further includes a second prismand a third prism. The second prism is in contact with the secondpolarization selective reflector, and the third prism is in contact withthe first polarization selective reflector.

In some embodiments, the first polarization selective reflector isconfigured to direct first light having a first nonplanar polarization(e.g., a circular polarization or an elliptical polarization) toward thesecond polarization selective reflector and the second polarizationselective reflector is configured to direct second light having a secondnonplanar polarization toward the first polarization selectivereflector.

In some embodiments, the first polarization selective reflector isconfigured to direct first light having a first nonplanar polarization(e.g., a circular polarization or an elliptical polarization) toward thesecond polarization selective reflector and the second polarizationselective reflector is configured to direct second light having a secondnonplanar polarization toward the first polarization selectivereflector.

In some embodiments, at least one of the first polarization selectivereflector or the second polarization selective reflector is either (i) aliquid crystal based polarization selective element, or (ii) apolarization selective element that includes a metasurface, resonantstructures, a chiral layer, or a birefringent material.

In some embodiments, the first angle is an acute angle, the first angleis measured from a portion of the first plane that directs the firstlight to a portion of the second plane that directs the second light,and the first polarization selective reflector is disposed along adiagonal of the optical device.

In accordance to some embodiments, a method includes coupling a firstpolarization selective reflector to a second polarization selectivereflector so that a first plane defined by the first polarizationselective reflector intersects, at a first angle, a second plane definedby the second polarization selective reflector so that the firstpolarization selective reflector is configured to direct first lighthaving a first polarization toward the second polarization selectivereflector and the second polarization selective reflector is configuredto direct second light having a second polarization toward the firstpolarization selective reflector.

In some embodiments, coupling the first polarization selective reflectorto the second polarization selective reflector includes disposing thesecond polarization selective reflector on a first surface of a prismand disposing the second polarization selective reflector on a secondsurface of the prism. In some embodiments, the first angle isapproximately 90 degrees; and the first polarization is identical to thesecond polarization. In some embodiments, the angle is more or less than90 degrees.

In some embodiments, coupling the first polarization selective reflectorto the second polarization selective reflector includes disposing thefirst polarization selective reflector on a first surface of a firstprism and disposing the second polarization selective reflector on asecond surface of the first prism. The first angle is an acute angle,and the method also includes attaching a second prism to the firstsurface of the first prism so that the first polarization selectivereflector is disposed along a diagonal of a prism assembly that includesthe first prism and the second prism.

In some embodiments, the first polarization selective reflector includesan element selected from the group consisting of a wire grid polarizer,a MacNeille polarizer, a liquid crystal based polarization selectiveelement, and a polarization element that includes a metasurface,resonant structures, or a chiral layer.

Thus, the disclosed embodiments provide devices and methods that providemore compact and lightweight head-mounted display devices.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the various described embodiments,reference should be made to the Description of Embodiments below, inconjunction with the following drawings in which like reference numeralsrefer to corresponding parts throughout the figures.

FIG. 1 is a perspective view of a display device in accordance with someembodiments.

FIG. 2 is a block diagram of a system including a display device inaccordance with some embodiments.

FIG. 3 is an isometric view of a display device in accordance with someembodiments.

FIG. 4A is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 4B is a schematic diagram illustrating optical paths of light froma spatial light modulator in the illumination system of FIG. 4A.

FIG. 4C is a schematic diagram of an illumination system in accordancewith some embodiments.

FIG. 4D is a schematic diagram comparing dimensions of polarizationselective reflectors in accordance with some embodiments.

FIG. 5 is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 6 is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIGS. 7A-7C illustrates methods for forming a first polarizationselective reflector and a second polarization selective reflector inaccordance with some embodiments.

FIG. 8A is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 8B is a schematic diagram illustrating a perspective view of theillumination system of FIG. 8A.

FIG. 9 is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 10A is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 10B is a schematic diagram illustrating an illumination system inaccordance with some embodiments.

FIG. 11A is a schematic diagram illustrating a projection system inaccordance with some embodiments.

FIG. 11B is a schematic diagram illustrating a projection system inaccordance with some embodiments.

FIG. 12 is a schematic diagram illustrating a projection system inaccordance with some embodiments.

FIG. 13A is a schematic diagram illustrating a projection system inaccordance with some embodiments.

FIG. 13B is a schematic diagram comparing side views and top views ofdifferent projection systems in accordance with some embodiments.

FIG. 14A is a schematic diagram illustrating a compact spatial lightmodulator having an illumination system in accordance with someembodiments.

FIG. 14B is a schematic diagram illustrating an optical path ofillumination light traversing a first polarization selective reflectorand a second polarization selective reflector in accordance with someembodiments.

FIG. 14C is a schematic diagram illustrating an optical path ofillumination light traversing a first polarization selective reflectorand a second polarization selective reflector in accordance with someembodiments.

FIG. 14D is a schematic diagram illustrating an optical path ofillumination light to a spatial light modulator in accordance with someembodiments.

FIG. 14E is a schematic diagram illustrating an optical path ofillumination light to a spatial light modulator in accordance with someembodiments.

FIG. 15A is a schematic diagram illustrating a compact spatial lightmodulator having an illumination system in accordance with someembodiments.

FIG. 15B is a schematic diagram illustrating a compact spatial lightmodulator having an illumination system in accordance with someembodiments.

FIGS. 16A-16D are schematic diagrams illustrating a polarization volumeholographic grating in accordance with some embodiments.

These figures are not drawn to scale unless indicated otherwise.

DETAILED DESCRIPTION

Reference will now be made to embodiments, examples of which areillustrated in the accompanying drawings. In the following description,numerous specific details are set forth in order to provide anunderstanding of the various described embodiments. However, it will beapparent to one of ordinary skill in the art that the various describedembodiments may be practiced without these specific details. In otherinstances, well-known methods, procedures, components, circuits, andnetworks have not been described in detail so as not to unnecessarilyobscure aspects of the embodiments.

It will also be understood that, although the terms first, second, etc.are, in some instances, used herein to describe various elements, theseelements should not be limited by these terms. These terms are used onlyto distinguish one element from another. For example, a first regioncould be termed a second region, and, similarly, a second region couldbe termed a first region, without departing from the scope of thevarious described embodiments. The first region and the second regionare both regions, but they are not the same region.

The terminology used in the description of the various describedembodiments herein is for the purpose of describing particularembodiments only and is not intended to be limiting. As used in thedescription of the various described embodiments and the appendedclaims, the singular forms “a,” “an,” and “the” are intended to includethe plural forms as well, unless the context clearly indicatesotherwise. It will also be understood that the term “and/or” as usedherein refers to and encompasses any and all possible combinations ofone or more of the associated listed items. It will be furtherunderstood that the terms “includes,” “including,” “comprises,” and/or“comprising,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof. The term “exemplary” is used herein in the senseof “serving as an example, instance, or illustration” and not in thesense of “representing the best of its kind.”

Embodiments described herein may include or be implemented inconjunction with an artificial reality system. Artificial reality is aform of reality that has been adjusted in some manner beforepresentation to a user, which may include, e.g., a virtual reality (VR),an augmented reality (AR), a mixed reality (MR), a hybrid reality, orsome combination and/or derivatives thereof. Artificial reality contentmay include completely generated content or generated content combinedwith captured (e.g., real-world) content. The artificial reality contentmay include video, audio, haptic feedback, or some combination thereof,and any of which may be presented in a single channel or in multiplechannels (such as stereo video that produces a three-dimensional effectto the viewer). Additionally, in some embodiments, artificial realitymay also be associated with applications, products, accessories,services, or some combination thereof, that are used to, e.g., createcontent in an artificial reality and/or are otherwise used in (e.g.,perform activities in) an artificial reality. The artificial realitysystem that provides the artificial reality content may be implementedon various platforms, including a head-mounted display (HMD) connectedto a host computer system, a standalone HMD, a mobile device orcomputing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

FIG. 1 illustrates display device 100 in accordance with someembodiments. In some embodiments, display device 100 is configured to beworn on the head of a user (e.g., by having the form of spectacles oreyeglasses, as shown in FIG. 1 ) or to be included as part of a helmetthat is to be worn by the user. When display device 100 is configured tobe worn on a head of a user or to be included as part of a helmet orheadset, display device 100 is called a head-mounted display.Alternatively, display device 100 is configured for placement inproximity of an eye or eyes of the user at a fixed location, withoutbeing head-mounted (e.g., display device 100 is mounted in a vehicle,such as a car or an airplane, for placement in front of an eye or eyesof the user). As shown in FIG. 1 , display device 100 includes display110. Display 110 is configured for presenting visual content (e.g.,augmented reality content, virtual reality content, mixed realitycontent, or any combination thereof) to a user.

In some embodiments, display device 100 includes one or more componentsdescribed below with respect to FIG. 2 . In some embodiments, displaydevice 100 includes additional components not shown in FIG. 2 .

FIG. 2 is a block diagram of system 200 in accordance with someembodiments. The system 200 shown in FIG. 2 includes display device 205(which corresponds to display device 100 shown in FIG. 1 ), imagingdevice 235, and input interface 240 that are each coupled to console210. While FIG. 2 shows an example of system 200 including one displaydevice 205, imaging device 235, and input interface 240, in otherembodiments, any number of these components may be included in system200. For example, there may be multiple display devices 205 each havingan associated input interface 240 and being monitored by one or moreimaging devices 235, with each display device 205, input interface 240,and imaging device 235 communicating with console 210. In alternativeconfigurations, different and/or additional components may be includedin system 200. For example, in some embodiments, console 210 isconnected via a network (e.g., the Internet) to system 200 or isself-contained as part of display device 205 (e.g., physically locatedinside display device 205). In some embodiments, display device 205 isused to create mixed reality by adding in a view of the realsurroundings. Thus, display device 205 and system 200 described here candeliver virtual reality, mixed reality, and/or augmented reality.

In some embodiments, as shown in FIG. 1 , display device 205 is ahead-mounted display that presents media to a user. Examples of mediapresented by display device 205 include one or more images, video,audio, haptics, or some combination thereof. In some embodiments, audiois presented via an external device (e.g., speakers and/or headphones)that receives audio information from display device 205, console 210, orboth, and presents audio data based on the audio information. In someembodiments, display device 205 immerses a user in a virtualenvironment.

In some embodiments, display device 205 also acts as an augmentedreality (AR) headset. In these embodiments, display device 205 canaugment views of a physical, real-world environment withcomputer-generated elements (e.g., images, video, sound, haptics, etc.).Moreover, in some embodiments, display device 205 is able to cyclebetween different types of operation. Thus, display device 205 operateas a virtual reality (VR) device, an AR device, as glasses or somecombination thereof (e.g., glasses with no optical correction, glassesoptically corrected for the user, sunglasses, or some combinationthereof) based on instructions from application engine 255.

Display device 205 includes electronic display 215, one or moreprocessors 216, eye tracking module 217, adjustment module 218, one ormore locators 220, one or more position sensors 225, one or moreposition cameras 222, memory 228, inertial measurement unit (IMU) 230,or a subset or superset thereof (e.g., display device 205 withelectronic display 215, one or more processors 216, and memory 228,without any other listed components). Some embodiments of display device205 have different modules than those described here. Similarly, thefunctions can be distributed among the modules in a different mannerthan is described here.

One or more processors 216 (e.g., processing units or cores) executeinstructions stored in memory 228. Memory 228 includes high-speed randomaccess memory, such as DRAM, SRAM, DDR RAM, or other random access solidstate memory devices; and may include non-volatile memory, such as oneor more magnetic disk storage devices, optical disk storage devices,flash memory devices, or other non-volatile solid state storage devices.Memory 228, or alternately the non-volatile memory device(s) withinmemory 228, includes a non-transitory computer readable storage medium.In some embodiments, memory 228 or the computer readable storage mediumof memory 228 stores programs, modules and data structures, and/orinstructions for displaying one or more images on electronic display215.

Electronic display 215 displays images to the user in accordance withdata received from console 210 and/or processor(s) 216. In variousembodiments, electronic display 215 may comprise a single adjustableelectronic display element or multiple adjustable electronic displayselements (e.g., a display for each eye of a user).

In some embodiments, the display element includes one or more lightemission devices and a corresponding array of emission intensity array.An emission intensity array is an array of electro-optic pixels,opto-electronic pixels, some other array of devices that dynamicallyadjust the amount of light transmitted by each device, or somecombination thereof. These pixels are placed behind one or more lenses.In some embodiments, the emission intensity array is an array of liquidcrystal based pixels in an LCD (a Liquid Crystal Display). Examples ofthe light emission devices include: an organic light emitting diode, anactive-matrix organic light-emitting diode, a light emitting diode, sometype of device capable of being placed in a flexible display, or somecombination thereof. The light emission devices include devices that arecapable of generating visible light (e.g., red, green, blue, etc.) usedfor image generation. The emission intensity array is configured toselectively attenuate individual light emission devices, groups of lightemission devices, or some combination thereof. Alternatively, when thelight emission devices are configured to selectively attenuateindividual emission devices and/or groups of light emission devices, thedisplay element includes an array of such light emission devices withouta separate emission intensity array.

One or more lenses direct light from the arrays of light emissiondevices (optionally through the emission intensity arrays) to locationswithin each eyebox and ultimately to the back of the user's retina(s).An eyebox is a region that is occupied by an eye of a user locatedproximite to display device 205 (e.g., a user wearing display device205) for viewing images from display device 205. In some cases, theeyebox is represented as a 10 mm×10 mm square. In some embodiments, theone or more lenses include one or more coatings, such as anti-reflectivecoatings.

In some embodiments, the display element includes an infrared (IR)detector array that detects IR light that is retro-reflected from theretinas of a viewing user, from the surface of the corneas, lenses ofthe eyes, or some combination thereof. The IR detector array includes anIR sensor or a plurality of IR sensors that each correspond to adifferent position of a pupil of the viewing user's eye. In alternateembodiments, other eye tracking systems may also be employed.

Eye tracking module 217 determines locations of each pupil of a user'seyes. In some embodiments, eye tracking module 217 instructs electronicdisplay 215 to illuminate the eyebox with IR light (e.g., via IRemission devices in the display element).

A portion of the emitted IR light will pass through the viewing user'spupil and be retro-reflected from the retina toward the IR detectorarray, which is used for determining the location of the pupil.Alternatively, the reflection off of the surfaces of the eye is alsoused to determine the location of the pupil. The IR detector array scansfor retro-reflection and identifies which IR emission devices are activewhen retro-reflection is detected. Eye tracking module 217 may use atracking lookup table and the identified IR emission devices todetermine the pupil locations for each eye. The tracking lookup tablemaps received signals on the IR detector array to locations(corresponding to pupil locations) in each eyebox. In some embodiments,the tracking lookup table is generated via a calibration procedure(e.g., user looks at various known reference points in an image and eyetracking module 217 maps the locations of the user's pupil while lookingat the reference points to corresponding signals received on the IRtracking array). As mentioned above, in some embodiments, system 200 mayuse other eye tracking systems than the embedded IR one described above.

Adjustment module 218 generates an image frame based on the determinedlocations of the pupils. In some embodiments, this sends a discreteimage to the display such that will tile subimages together thus acoherent stitched image will appear on the back of the retina.Adjustment module 218 adjusts an output (i.e. the generated image frame)of electronic display 215 based on the detected locations of the pupils.Adjustment module 218 instructs portions of electronic display 215 topass image light to the determined locations of the pupils. In someembodiments, adjustment module 218 also instructs the electronic displaynot to pass image light to positions other than the determined locationsof the pupils. Adjustment module 218 may, for example, block and/or stoplight emission devices whose image light falls outside of the determinedpupil locations, allow other light emission devices to emit image lightthat falls within the determined pupil locations, translate and/orrotate one or more display elements, dynamically adjust curvature and/orrefractive power of one or more active lenses in the lens (e.g.,microlens) arrays, or some combination thereof.

Optional locators 220 are objects located in specific positions ondisplay device 205 relative to one another and relative to a specificreference point on display device 205. A locator 220 may be a lightemitting diode (LED), a corner cube reflector, a reflective marker, atype of light source that contrasts with an environment in which displaydevice 205 operates, or some combination thereof. In embodiments wherelocators 220 are active (i.e., an LED or other type of light emittingdevice), locators 220 may emit light in the visible band (e.g., about400 nm to 750 nm), in the infrared band (e.g., about 750 nm to 1 mm), inthe ultraviolet band (about 100 nm to 400 nm), some other portion of theelectromagnetic spectrum, or some combination thereof.

In some embodiments, locators 220 are located beneath an outer surfaceof display device 205, which is transparent to the wavelengths of lightemitted or reflected by locators 220 or is thin enough to notsubstantially attenuate the wavelengths of light emitted or reflected bylocators 220. Additionally, in some embodiments, the outer surface orother portions of display device 205 are opaque in the visible band ofwavelengths of light. Thus, locators 220 may emit light in the IR bandunder an outer surface that is transparent in the IR band but opaque inthe visible band.

IMU 230 is an electronic device that generates calibration data based onmeasurement signals received from one or more position sensors 225.Position sensor 225 generates one or more measurement signals inresponse to motion of display device 205. Examples of position sensors225 include: one or more accelerometers, one or more gyroscopes, one ormore magnetometers, another suitable type of sensor that detects motion,a type of sensor used for error correction of IMU 230, or somecombination thereof. Position sensors 225 may be located external to IMU230, internal to IMU 230, or some combination thereof.

Based on the one or more measurement signals from one or more positionsensors 225, IMU 230 generates first calibration data indicating anestimated position of display device 205 relative to an initial positionof display device 205. For example, position sensors 225 includemultiple accelerometers to measure translational motion (forward/back,up/down, left/right) and multiple gyroscopes to measure rotationalmotion (e.g., pitch, yaw, roll). In some embodiments, IMU 230 rapidlysamples the measurement signals and calculates the estimated position ofdisplay device 205 from the sampled data. For example, IMU 230integrates the measurement signals received from the accelerometers overtime to estimate a velocity vector and integrates the velocity vectorover time to determine an estimated position of a reference point ondisplay device 205. Alternatively, IMU 230 provides the sampledmeasurement signals to console 210, which determines the firstcalibration data. The reference point is a point that may be used todescribe the position of display device 205. While the reference pointmay generally be defined as a point in space; however, in practice thereference point is defined as a point within display device 205 (e.g., acenter of IMU 230).

In some embodiments, IMU 230 receives one or more calibration parametersfrom console 210. As further discussed below, the one or morecalibration parameters are used to maintain tracking of display device205. Based on a received calibration parameter, IMU 230 may adjust oneor more IMU parameters (e.g., sample rate). In some embodiments, certaincalibration parameters cause IMU 230 to update an initial position ofthe reference point so it corresponds to a next calibrated position ofthe reference point. Updating the initial position of the referencepoint as the next calibrated position of the reference point helpsreduce accumulated error associated with the determined estimatedposition. The accumulated error, also referred to as drift error, causesthe estimated position of the reference point to “drift” away from theactual position of the reference point over time.

Imaging device 235 generates calibration data in accordance withcalibration parameters received from console 210. Calibration dataincludes one or more images showing observed positions of locators 220that are detectable by imaging device 235. In some embodiments, imagingdevice 235 includes one or more still cameras, one or more videocameras, any other device capable of capturing images including one ormore locators 220, or some combination thereof. Additionally, imagingdevice 235 may include one or more filters (e.g., used to increasesignal to noise ratio). Imaging device 235 is optionally configured todetect light emitted or reflected from locators 220 in a field of viewof imaging device 235. In embodiments where locators 220 include passiveelements (e.g., a retroreflector), imaging device 235 may include alight source that illuminates some or all of locators 220, whichretroreflect the light towards the light source in imaging device 235.Second calibration data is communicated from imaging device 235 toconsole 210, and imaging device 235 receives one or more calibrationparameters from console 210 to adjust one or more imaging parameters(e.g., focal length, focus, frame rate, ISO, sensor temperature, shutterspeed, aperture, etc.).

Input interface 240 is a device that allows a user to send actionrequests to console 210. An action request is a request to perform aparticular action. For example, an action request may be to start or endan application or to perform a particular action within the application.Input interface 240 may include one or more input devices. Example inputdevices include: a keyboard, a mouse, a game controller, data from brainsignals, data from other parts of the human body, or any other suitabledevice for receiving action requests and communicating the receivedaction requests to console 210. An action request received by inputinterface 240 is communicated to console 210, which performs an actioncorresponding to the action request. In some embodiments, inputinterface 240 may provide haptic feedback to the user in accordance withinstructions received from console 210. For example, haptic feedback isprovided when an action request is received, or console 210 communicatesinstructions to input interface 240 causing input interface 240 togenerate haptic feedback when console 210 performs an action.

Console 210 provides media to display device 205 for presentation to theuser in accordance with information received from one or more of:imaging device 235, display device 205, and input interface 240. In theexample shown in FIG. 2 , console 210 includes application store 245,tracking module 250, and application engine 255. Some embodiments ofconsole 210 have different modules than those described in conjunctionwith FIG. 2 . Similarly, the functions further described below may bedistributed among components of console 210 in a different manner thanis described here.

When application store 245 is included in console 210, application store245 stores one or more applications for execution by console 210. Anapplication is a group of instructions, that when executed by aprocessor, is used for generating content for presentation to the user.Content generated by the processor based on an application may be inresponse to inputs received from the user via movement of display device205 or input interface 240. Examples of applications include: gamingapplications, conferencing applications, video playback application, orother suitable applications.

When tracking module 250 is included in console 210, tracking module 250calibrates system 200 using one or more calibration parameters and mayadjust one or more calibration parameters to reduce error indetermination of the position of display device 205. For example,tracking module 250 adjusts the focus of imaging device 235 to obtain amore accurate position for observed locators on display device 205.Moreover, calibration performed by tracking module 250 also accounts forinformation received from IMU 230. Additionally, if tracking of displaydevice 205 is lost (e.g., imaging device 235 loses line of sight of atleast a threshold number of locators 220), tracking module 250re-calibrates some or all of system 200.

In some embodiments, tracking module 250 tracks movements of displaydevice 205 using second calibration data from imaging device 235. Forexample, tracking module 250 determines positions of a reference pointof display device 205 using observed locators from the secondcalibration data and a model of display device 205. In some embodiments,tracking module 250 also determines positions of a reference point ofdisplay device 205 using position information from the first calibrationdata. Additionally, in some embodiments, tracking module 250 may useportions of the first calibration data, the second calibration data, orsome combination thereof, to predict a future location of display device205. Tracking module 250 provides the estimated or predicted futureposition of display device 205 to application engine 255.

Application engine 255 executes applications within system 200 andreceives position information, acceleration information, velocityinformation, predicted future positions, or some combination thereof ofdisplay device 205 from tracking module 250. Based on the receivedinformation, application engine 255 determines content to provide todisplay device 205 for presentation to the user. For example, if thereceived information indicates that the user has looked to the left,application engine 255 generates content for display device 205 thatmirrors the user's movement in a virtual environment. Additionally,application engine 255 performs an action within an applicationexecuting on console 210 in response to an action request received frominput interface 240 and provides feedback to the user that the actionwas performed. The provided feedback may be visual or audible feedbackvia display device 205 or haptic feedback via input interface 240.

FIG. 3 is an isometric view of display device 300 in accordance withsome embodiments. In some other embodiments, display device 300 is partof some other electronic display (e.g., digital microscope, etc.). Insome embodiments, display device 300 includes light emission devicearray 310 and one or more lenses 330. In some embodiments, displaydevice 300 also includes an emission intensity array and an IR detectorarray.

Light emission device array 310 emits image light and optional IR lighttoward the viewing user. Light emission device array 310 may be, e.g.,an array of LEDs, an array of microLEDs, an array of OLEDs, or somecombination thereof. Light emission device array 310 includes lightemission devices 320 that emit light in the visible light (andoptionally includes devices that emit light in the IR). In someembodiments, a microLED includes an LED with an emission areacharacterized by a representative dimension (e.g., a diameter, a width,a height, etc.) of 100 μm or less (e.g., 50 μm, 20 μm, etc.). In someembodiments, a microLED has an emission area having a shape of a circleor a rectangle.

The emission intensity array is configured to selectively attenuatelight emitted from light emission device array 310. In some embodiments,the emission intensity array is composed of a plurality of liquidcrystal cells or pixels, groups of light emission devices, or somecombination thereof. Each of the liquid crystal cells is, or in someembodiments, groups of liquid crystal cells are, addressable to havespecific levels of attenuation. For example, at a given time, some ofthe liquid crystal cells may be set to no attenuation, while otherliquid crystal cells may be set to maximum attenuation. In this mannerthe emission intensity array is able to control what portion of theimage light emitted from light emission device array 310 is passed tothe one or more lenses 330. In some embodiments, display device 300 usesthe emission intensity array to facilitate providing image light to alocation of pupil 350 of eye 340 of a user, and minimize the amount ofimage light provided to other areas in the eyebox.

One or more lenses 330 receive the modified image light (e.g.,attenuated light) from the emission intensity array (or directly fromlight emission device array 310), and shifted by one or more beamshifters 360, and direct the shifted image light to a location of pupil350.

An optional IR detector array detects IR light that has beenretro-reflected from the retina of eye 340, a cornea of eye 340, acrystalline lens of eye 340, or some combination thereof. The IRdetector array includes either a single IR sensor or a plurality of IRsensitive detectors (e.g., photodiodes). In some embodiments, the IRdetector array is separate from light emission device array 310. In someembodiments, the IR detector array is integrated into light emissiondevice array 310.

In some embodiments, light emission device array 310 and the emissionintensity array make up a display element. Alternatively, the displayelement includes light emission device array 310 (e.g., when lightemission device array 310 includes individually adjustable pixels)without the emission intensity array. In some embodiments, the displayelement additionally includes the IR array. In some embodiments, inresponse to a determined location of pupil 350, the display elementadjusts the emitted image light such that the light output by thedisplay element is refracted by one or more lenses 330 toward thedetermined location of pupil 350, and not toward other locations in theeyebox.

FIG. 4A is a schematic diagram illustrating an illumination system 400in accordance with some embodiments. In some embodiments, theillumination system 400 is included in a head-mounted display device.

In FIG. 4A, the illumination system 400 includes a first polarizationselective reflector 410, a second polarization selective reflector 420,a mirror 430 (e.g., a retroreflector), and a phase retarder 440 (e.g., apolarization retarder or a waveplate, such as a quarter-wave plate). Theillumination system 400 is optically coupled with (e.g., positionedrelative to) a spatial light modulator 452 that has a first portion 454and a second portion 456 so that the illumination system 400 illuminatesthe spatial light modulator 452. In some embodiments, the illuminationsystem 400 is positioned to receive light from one or more light sources408. In some embodiments, the illumination system 400 includes the oneor more light sources 408.

In some embodiments, the illumination system 400 is optically coupledwith (e.g., positioned relative to) a projection system 450 (e.g., aprojection lens, a projection lens assembly) so that the projectionsystem 450 receives light (e.g., image light) output from theillumination system 400 and projects the light (e.g., to an eyebox of auser of the head-mounted display device). In some embodiments, couplingoptics (e.g., waveguides, lenses, etc.) are used to couple an output ofthe projection system 450 to the eyebox.

In some embodiments, one or more of polarization selective reflectors410 and 420 are partial reflectors. “Partial reflectors” include opticalelements that fully reflect (e.g., with a reflectivity greater than 90%,95%, or 99%) light of one polarization (e.g., a reflective polarizer)while transmitting at least a portion (e.g., at least 10%, 20%, 50%,70%, 80%, or 90%) of light having an orthogonal polarization. In someembodiments, the one or more light sources 408 provide light 462 havingorthogonally polarized components (e.g., a combination of ans-polarization component and a p-polarization component). For example,the light 462 may be diagonally polarized, circularly polarized,elliptically polarized, or unpolarized.

In FIG. 4A, the light 462 includes a first polarization component inwhich the electric field lies in the x-z plane (which is called herein“vertically polarized” or “having vertical polarization” for ease ofreference), and a second polarization component in which the electricfield lies in the z-y plane (which is called herein “horizontallypolarized” or “having horizontal polarization for ease of reference).

The first polarization selective reflector 410 is positioned in a firstorientation (e.g., making an acute angle with respect to the z-y plane,such as a 45° angle with respect to the z-y plane) and receives thelight 462 in a first direction (e.g., along the +z direction). In someembodiments, the first polarization selective reflector 410 isconfigured to reflect light that is horizontally polarized and transmitlight that is vertically polarized. In some embodiments, the firstpolarization selective reflector 410 includes a wire grid polarizer. Insome embodiments, the first polarization selective reflector 410includes a MacNeille polarizer. In some embodiments, the firstpolarization selective reflector 410 includes a liquid crystal basedpolarization selective element. In some embodiments, a polarizationelement includes a metasurface, resonant structures, or a chiral layer.

In some embodiments, the first polarization selective reflector 410redirects the first portion (e.g., light 464) of the light 462, having afirst polarization (e.g., horizontal polarization) to a second direction(e.g., −x direction), that is non-parallel to the first direction (e.g.,+z direction). For example, the first polarization selective reflector410 is positioned to reflect the first portion (e.g., the portion thatis horizontally polarized) of the light 462 as light 464, toward thespatial light modulator 452. In some embodiments, the second direction(e.g., −x direction) is orthogonal to the first direction (e.g., +zdirection).

In some embodiments, the spatial light modulator 452 receives the light464 and depending on the setting for a particular location (e.g., pixel)of the spatial light modulator 452, modifies the light 464 (or at leasta portion of the light 464 that impinges on the particular location ofthe spatial light modulator 452), and provides (e.g., reflects) themodified light as light 482 having a polarization different from thepolarization of the light 464 towards the first polarization selectivereflector 410. For example, the light 464, which is horizontallypolarized, is modified by the spatial light modulator 452 to becomelight 482 that is vertically polarized. Although the light 482 reflectsfrom the spatial light modulator 452 at or close to a location where thelight 464 strikes the spatial light modulator 452, in FIG. 4A, the light482 is shown offset from the light 464 in the z-direction for ease ofreference. The first polarization selective reflector 410 receivessecond light (e.g., light 482) in a third direction (e.g., +x direction)and transmits at least a first portion (e.g., light 484) of the secondlight, having a second polarization (e.g., vertical polarization)orthogonal to the first polarization (e.g., horizontal polarization).The vertically polarized light 482 directed toward the firstpolarization selective reflector 410 is transmitted through the firstpolarization selective reflector 410 as light 484 because of itspolarization. The light 484, having a vertical polarization, then entersthe projection system 450.

In some embodiments, the first polarization selective reflector 410 isfurther configured to transmit a second portion (e.g., light 466), ofthe first light, having the second polarization (e.g., verticallypolarized). In some embodiments, the first polarization selectivereflector 410 transmits a second portion (e.g., the portion that isvertically polarized) of the light 462 as the light 466, toward thesecond polarization selective reflector 420. In some embodiments, thesecond polarization selective reflector 420 is configured (e.g.,positioned) to receive the second portion (e.g., the light 466) of thefirst light having the second polarization (e.g., vertically polarized).

In some embodiments, the first polarization selective reflector 410 andthe second polarization selective reflector 420 both reflect lighthaving horizontal polarization and transmit light having verticalpolarization. In some embodiments, the second polarization selectivereflector 420 is configured (e.g., positioned) to transmit the secondportion (e.g., the light 466) of the first light having the secondpolarization (e.g., vertically polarized). For example, the secondpolarization selective reflector 420 may include one or more of: a wiregrid polarizer, a MacNeille polarizer, a liquid crystal basedpolarization selective element, or a polarization element including ametasurface, resonant structures, or a chiral layer. In someembodiments, the vertically polarized light 466 is transmitted throughthe second polarization selective reflector 420 and maintains itsvertical polarization as light 468.

In some embodiments, the light 468 (e.g., linearly polarized light, suchas vertically polarized light) is incident on the phase retarder 440 ata particular incident angle (e.g., 0°). In some embodiments, the phaseretarder 440 is a quarter-wave plate configured to convert the linearlypolarized light 468 to circularly polarized light 470 (e.g.,left-circularly polarized light) and transmits the circularly polarizedlight 470 toward the mirror 430. In general, phase retarders can includedifferent types of waveplates, but hereinafter, a quarter-wave plate isused as an example of the phase retarder 440. The quarter-wave plate 440has its fast axis oriented such that a first portion of the verticallypolarized light 468 accumulates a phase shift of 90° with respect to asecond portion of the vertically polarized light 468, creating thecircularly polarized light 470.

In some embodiments, the illumination system 400 includes a thirdreflector (e.g., the mirror 430) configured to receive from the secondpolarization selective reflector 420 the second portion (e.g., the light468) of the first light, and redirect the second portion of the firstlight back to the second polarization selective reflector 420 as thesecond light (e.g., light 474). For example, in configurations with thephase retarder 440 (e.g., a quarter-wave plate), the mirror 430 reflectsthe circularly polarized light 470 toward the phase retarder 440 aslight 472. When the circularly polarized light 470 is reflected by themirror 430, a direction in which the electric field vector of thecircularly polarized light 470 rotates is reversed. Thus, the circularlypolarized light 472 (e.g., left-circularly polarized light) has ahandedness opposite to the circularly polarized light 470 (e.g.,right-circularly polarized light). As the circularly polarized light 472passes through the phase retarder 440, the phase retarder 440 convertsthe circularly polarized light 472 to linearly polarized light 474 andtransmit the linearly polarized light 474 toward the second polarizationselective reflector 420. In some embodiments, a plane of vibration ofthe linearly polarized light 474 (e.g., horizontally polarized) isperpendicular to a plane of vibration of the linearly polarized light466 (e.g., vertically polarized), and the second polarization selectivereflector 420 reflects the linearly polarized light 474 toward thespatial light modulator 452 as light 476.

In some embodiments, the second polarization selective reflector 420 ispositioned in a second orientation (e.g., making an acute angle withrespect to the z-y plane, such as a 45° angle with respect to the z-yplane) non-parallel to the first orientation, and adjacent to the firstpolarization selective reflector 410 (e.g., one end of the secondpolarization selective reflector 420 is in contact with one end of thefirst polarization selective reflector 410). The second polarizationselective reflector 420 receives third light (e.g., light 474) in afourth direction (e.g., −z direction), redirects a first portion (e.g.,light 476) of the third light having the first polarization (e.g.,horizontally polarized light) to a fifth direction (e.g., −x direction)that is non-parallel to the fourth direction (−z direction).

The spatial light modulator 452 modifies a polarization of thehorizontally polarized light 476 to provide light 478 that is verticallypolarized, and directs the light 478 toward the second polarizationselective reflector 420. The second polarization selective reflector 420receives fourth light (e.g., light 478) in a sixth direction (e.g., +xdirection) and transmits at least a first portion (e.g., light 480) ofthe fourth light having the second polarization (e.g., verticalpolarization). The light 480, having the same polarization (e.g., avertical polarization) as the light 484, then enters the projectionsystem 450.

Light that reflects off the first polarization selective reflector 410(e.g., light 464) is incident on the first portion 454 of the spatiallight modulator 452. In contrast, at least a portion of the light thattransmits through the first polarization selective reflector 410 (e.g.,light 476) is incident on the second portion 456 of the spatial lightmodulator 452. Thus, in some embodiments, the first portion 454 of thespatial light modulator 452 is configured to modify or manipulate acomponent of the light 462 having a first polarization (e.g., horizontalpolarization) only, while the second portion 456 of the spatial lightmodulator 452 is configured to modify or manipulate a component of thelight 462 having a second polarization (e.g., vertical polarization)only. In some embodiments, the light 462 is selectively encoded withcertain proportions of vertically polarized light and horizontallypolarized light (e.g., a vertically polarized component and ahorizontally polarized component have a certain intensity ratio).

In some embodiment, the spatial light modulator 452 modifies apolarization state of at least a portion of light reflected by thespatial light modulator 452, and at least a portion of the reflectedlight is transmitted by first polarization selective reflector 410 andthe second polarization selective reflector 420 (e.g., as light 484 andlight 480, respectively), and is imaged by the projection system 450. Insome embodiments, the projection lens 450 directs the light (e.g., light480 and light 484) to an image combiner, such as a partially reflectivesurface, a reflective polarizer, a polarization volume hologram(described with respect to FIGS. 16A-16D), or a holographic opticalelement.

In some embodiments, the spatial light modulator 452 is a Liquid Crystalon Silicon (LCoS) spatial light modulator. In some embodiments, LCoS isbased on liquid crystal. In some embodiments, LCoS is based onferroelectric liquid crystal.

In some embodiments, at least a portion of light reflected by firstpolarization selective reflector 410 and the second polarizationselective reflector 420 is redirected back to the illumination source.In some embodiments, the redirected light is recycled to improve theefficiency of the illumination system 400.

In some cases, non-uniformity of an illumination pattern (e.g.,non-uniformity in illumination intensities across the spatial lightmodulator 452) contributes to non-uniformity (or irregularity) in animage provided by the spatial light modulator 452. In some embodiments,the non-uniformity in the image is reduced by adjusting operations(e.g., reflectivities or magnitudes of phase retardation) of the spatiallight modulator 452 based on, for example, a look-up pattern for theimage created by the spatial light modulator 452 to compensate forvariations in illumination intensities.

Although FIG. 4A shows the light 462 as a single ray of light so as notto obscure other aspects of FIG. 4A, in some embodiments, the light 462has a beam height that is equal to or smaller than a height 402 of thefirst polarization selective reflector 410, along the x-direction. Abeam having a beam height in the x-direction that corresponds to theheight 402 may substantially fill a first portion 454 of the spatiallight modulator 452. In some embodiments, instead of a single beamhaving a beam height corresponding to height 402, the one or more lightsources 408 provide one or more beams offset along the x-directiontoward the first polarization selective reflector 410. In someembodiments, the one or more beams are substantially parallel to oneanother. In some embodiments, the light 462 has a beam width that isequal to or smaller than a width of the first polarization selectivereflector 410, along the y-direction. A beam having a beam width in they-direction that corresponds to the width of the first polarizationselective reflector 410 may substantially fill a first portion 454 ofthe spatial light modulator 452. In some embodiments, instead of asingle beam having a beam width corresponding to the width of the firstpolarization selective reflector 410, the one or more light sources 408provide one or more beams offset along the y-direction toward the firstpolarization selective reflector 410.

In some embodiments, the first and second polarization selectivereflectors 410 and 420 are included in two beam splitter blocks (e.g.,the first polarization selective reflector 410 is included in a firstbeam splitter block and the second polarization selective reflector 420is included in a second beam splitter block).

In some embodiments, each beam splitter block has a shape of arectangular prism (e.g., a cuboid). In some embodiments, the rectangularprism has a square cross section. In some embodiments, a polarizationselective reflector is embedded diagonally in each rectangular prism.

In some embodiments, each beam splitter block has a shape of atriangular prism. In some embodiments, the triangular prism has a righttriangle cross section. In some embodiments, a polarization selectivereflector is located on a slope facet of each triangular prism(corresponding to the hypotenuse of the right triangle cross section).

In some embodiments, the two beam splitter blocks are bonded togetherusing an optical coupling layer with a refractive index that is lessthan 0.05 (e.g., less than 0.05, less than 0.04, less than 0.03, lessthan 0.02, or less than 0.01) of the material (e.g., glass) of the beamsplitters.

In some embodiments, the first and second polarization selectivereflectors 410 and 420 are located on slopes of a beam splitter blockhaving a shape of a triangular prism, as shown in FIG. 8B. In someembodiments, the triangular prism has an isosceles cross section.

In some embodiments, the first polarization selective reflector 410 andthe second polarization selective reflector 420 (or the beam splitterblocks) have an effectively uniform refractive index. In some cases,effectively uniform refractive index means that refractive indices ofthe first and second polarization selective reflectors 410 and 420differ by less than 0.05 (e.g., less than 0.04, less than 0.03, lessthan 0.02, or less than 0.01). In particular, the term includes a casewhere there is no difference in refractive indices of the first andsecond polarization selective reflectors 410 and 420 (or the beamsplitter blocks) so that the first polarization selective reflector 410or the second polarization selective reflector 420 do not causerefraction or total internal reflection for light impinging on the firstpolarization selective reflector 410 or the second polarizationselective reflector 420 (e.g., at an angle of about 45° to the firstpolarization selective reflector 410 or the second polarizationselective reflector 420).

FIG. 4B is a schematic diagram illustrating optical paths of light froma spatial light modulator in the illumination system of FIG. 4A. Asdescribed with respect to FIG. 4A, when the reflective spatial lightmodulator 452 is illuminated, the spatial light modulator 452 modifies apolarization of the light incident thereon and provides (e.g., reflects)light having the modified polarization toward the first polarizationselective reflector 410 and the second polarization selective reflector420. In some embodiments, when the light provided by the spatial lightmodulator 452 (e.g., light 483 and 479) has components of orthogonalpolarizations, the first and second polarization selective reflectors410 and 420 transmit portions of light incident thereon and reflectportions of light incident thereon.

For example, the first portion 454 of the spatial light modulator 452directs the light 483 having a mixture of vertically polarized light andhorizontally polarized light to the first polarization selectivereflector 410 (unlike the light 482 in FIG. 4A, which is verticallypolarized). The first polarization selective reflector 410 reflects thehorizontally polarized component of the light 483 as light 486 towardthe one or more light sources 408 to recycle the light and improve anefficiency of the illumination system. The vertically polarizedcomponent of the light 483 is transmitted through the first polarizationselective reflector 410 as light 485, and enters the projection system450 as vertically polarized light. The second portion 456 of the spatiallight modulator 452 directs the light 479 having a mixture of verticallypolarized light and horizontally polarized light to the secondpolarization selective reflector 420 (unlike the light 478 in FIG. 4A,which is vertically polarized). The vertically polarized component ofthe light 479 is transmitted through the second polarization selectivereflector 420 as light 481, and enters the projection system 450 asvertically polarized light. The second polarization selective reflector420 reflects the horizontally polarized component of the light 479 aslight 488 toward the phase retarder 440. The light 488 maintains itshorizontal polarization as it reflects off the second polarizationselective reflector 420. The phase retarder 440, which is a quarter-waveplate in some embodiments, converts the linearly polarized light 488into circularly polarized light 489 and transmit the light 489 towardthe mirror 430. The mirror 430 reflects the circularly polarized light489 back toward the phase retarder 440 as light 491. When the circularlypolarized light 489 is reflected by the mirror 430, a direction in whichthe electric field vector of the circularly polarized light 489 rotatesis reversed. Thus, the circularly polarized light 491 transmitted towardthe phase retarder 440 has a handedness (e.g., right-circularlypolarized light) opposite to the circularly polarized light 489 (e.g.,left-circularly polarized light). As the circularly polarized light 491passes through the phase retarder 440, the phase retarder 440 convertsthe circularly polarized light 491 to linearly polarized light 490(e.g., having vertical polarization) and transmits light 490 toward thesecond polarization selective reflector 420. In some embodiments, aplane of vibration of the linearly polarized light 490 (e.g., verticallypolarized) is perpendicular to a plane of vibration of the linearlypolarized light 488 (e.g., horizontally polarized), and the secondpolarization selective reflector 420 transmits the linearly polarizedlight 490 toward the first polarization selective reflector 410 as light492. The first polarization selective reflector 410 transmits the light492 as vertically polarized light 494 toward the one or more lightsources 408 for recycling of the light.

In some embodiments, as shown in FIG. 4A, a first plane defined by thefirst polarization selective reflector 410 and a second plane defined bythe second polarization selective reflector 420 intersect at an angle406. In some embodiments, the angle 406 is substantially 90° (e.g.,between 80° and 100°, between 85° and 95°, between 87° and 93°, orbetween 89° and 91°). In some embodiments, the angle 406 is 90°.

FIG. 4C shows a first polarization selective reflector 412 positioned atan angle 407 with respect to a second polarization selective reflector422, where the angle 407 is different from the angle 406 shown in FIG.4A. In some embodiments, an angle 407 is greater than 90°. In someembodiments, an angle 407 is less than 90°.

Even though FIG. 4A shows the light 464 having a 45° incident angle,light from the one or more light sources 408 may have an incident angleother than 45°. In FIG. 4C, the light 462 is incident on the firstpolarization selective reflector 412 at an incident angle that is largerthan 45°, and the light 464 is incident on the spatial light modulator452 at an angle that differs from normal incidence (e.g., the light 464has an incident angle that is different from 0°, which is normalincidence). Similarly, light 476, reflected by the second polarizationselective reflector 422 is incident on the spatial light modulator 452at an angle that differs from normal incidence.

In some embodiments, the first polarization selective reflector 412 isnot in direct contact with the second polarization selective reflector422. In some embodiments, the first polarization selective reflector 412is mechanically supported independently from the second polarizationselective reflector 422.

FIG. 4D illustrates how a combination of the first polarizationselective reflector (e.g., 410) and the second polarization selectivereflector (e.g., 420) enables a more compact illumination system byreducing a volume and a height of optical components (e.g., polarizingbeam splitter(s)) compared to illumination systems that use a singlepolarization selective reflector. When the first polarization selectivereflector 410 and the second polarization selective reflector 420(having 90° between the two while each polarization selective reflectortilted 45° relative to the spatial light modulator 452) are used toilluminate the spatial light modulator 452 having a length 404 along thez-direction, the first polarization selective reflector 410 and thesecond polarization selective reflector 420 have a height 402. Incomparison, when a single polarization selective reflector 490 (tilted45° relative to the spatial light modulator 452) is used to illuminatethe spatial light modulator 452 having the same length 404, the singlepolarization selective reflector 490 needs to have a height 493 greaterthan the height 402. In fact, the height 493 is twice the height 402,regardless of the magnitude of the angle, as long as the singlepolarization selective reflector and the pair of polarization selectivereflectors are tilted relative to the spatial light modulator 452 by asame angle (e.g., when the first and second polarization selectivereflectors 410 and 420 form a 120° angle, and each of the singlepolarization selective reflector 490 and the first and secondpolarization selective reflectors 410 and 420 is tilted by 30° relativeto the spatial light modulator 452). Thus, replacing the singlepolarization selective reflector 490 with the pair of the firstpolarization selective reflector 410 and the second polarizationselective reflector 420 allows reducing the height of the opticalcomponents by half.

In addition, in configurations, in which a respective polarizationselective reflector is sandwiched and supported by a pair of right angletriangular prisms, a total volume of the right angle triangular prismsembedding the single polarization selective reflector 490 would be twotime greater than a total volume of triangular prisms embedding thefirst polarization selective reflector 410 and the second polarizationselective reflector 420. Thus, replacing the single polarizationselective reflector 490 with the pair of the first polarizationselective reflector 410 and the second polarization selective reflector420 also allows reducing the total weight of the optical components byhalf.

FIG. 5 shows an illumination system 500, which is similar to theillumination system 400 except that the illumination system 500 includesa first polarization selective reflector 414 and a second polarizationselective reflector 424 instead of the first polarization selectivereflector 410 and the second polarization selective reflector 420. Thefirst polarization selective reflector 414 reflects vertically polarizedlight, and transmits horizontally polarized light, unlike the firstpolarization selective reflector 410, which reflects horizontallypolarized light and transmits vertically polarized light.

As explained above with respect to FIG. 4A, the light 462 containsorthogonally polarized components. For example, the light 462 may bediagonally polarized, circularly polarized, elliptically polarized, orunpolarized.

The first polarization selective reflector 414 reflects a first portion(e.g., the portion that is vertically polarized) of the light 462incident on the first polarization selective reflector 414 as light 502,toward the spatial light modulator 452. The spatial light modulator 452receives the light 502, and depending on a setting for a particularlocation (e.g., pixel) of the spatial light modulator 452, modifies thelight 502 (or a portion of the light 502 that impinges on the particularlocation of the spatial light modulator 452), and provides (e.g.,reflects) the modified light as light 504 having a polarizationdifferent from the polarization of the light 502 towards the firstpolarization selective reflector 414. For example, the light 502, whichis vertically polarized is modified by the spatial light modulator 452to become the light 504 that is horizontally polarized. Similar to FIG.4A, in FIG. 5 , the light 502 is shown offset from the light 504 alongthe z-direction, even though the light 504 reflects from the spatiallight modulator 452 at or close to a location where the light 502strikes the spatial light modulator 452. The horizontally polarizedlight 504 directed toward the first polarization selective reflector 414is transmitted through the first polarization selective reflector 414 aslight 506 (as the first polarization selective reflector 414 isconfigured to transmit horizontally polarized light). The light 506 thenenters the projection system 450.

The first polarization selective reflector 414 transmits a secondportion (e.g., the portion that is horizontally polarized) of the light462 as light 508, toward the second polarization selective reflector424. In some embodiments, the first polarization selective reflector 414and the second polarization selective reflector 424 both reflect lighthaving vertical polarization and transmit light having horizontalpolarization. The horizontally polarized light 508 is transmittedthrough the second polarization selective reflector 424 and maintainsits horizontal polarization as light 510. In some embodiments, thelinearly polarized light 510 is incident on the phase retarder 440 at aparticular incident angle (e.g., less than 10° or 5°, such as 0°). Insome embodiments, the phase retarder 440 is a quarter-wave plateconfigured to convert the linearly polarized light 510 to circularlypolarized light 512 (e.g., right-circularly polarized light) andtransmit the circularly polarized light 512 toward the mirror 430. Forexample, the quarter-wave plate may have its fast axis oriented suchthat a first portion of the vertically polarized light 510 accumulates aphase shift of 90° with respect to a second portion of the verticallypolarized light 510, creating the circularly polarized light 512.

The mirror 430 reflects the circularly polarized light 512 toward thephase retarder 440 as light 514. When the circularly polarized light 512is reflected by the mirror 430, a direction in which the electric fieldvector of the circularly polarized light 514 rotates is reversed. Thus,the circularly polarized light 514 transmitted toward the phase retarder440 has a handedness (e.g., left-circular polarization) opposite to thecircularly polarized light 512 (e.g., right-circular polarization). Asthe circularly polarized light 514 passes through the phase retarder440, the phase retarder 440 converts the circularly polarized light 514to linearly polarized light 516 and transmit the linearly polarizedlight 516 toward the second polarization selective reflector 424. Insome embodiments, a plane of vibration of the linearly polarized light516 (e.g., vertically polarized) is perpendicular to a plane ofvibration of the linearly polarized light 510 (e.g., horizontallypolarized) and the second polarization selective reflector 424 reflectsthe linearly polarized light 516 toward the spatial light modulator 452as light 518. The spatial light modulator 452 modifies a polarization ofthe vertically polarized light 518 to form light 520 that ishorizontally polarized, and directs the light 520 toward the secondpolarization selective reflector 424. The horizontally polarized light520 is transmitted through the second polarization selective reflector424 as light 522, which maintains its horizontal polarization. The light522, which is horizontally polarized, then enters the projection system450.

In addition to plane-polarized light (e.g., linearly polarized light,light having planar polarizations), in some embodiments, the first andsecond polarization selective reflectors transmit and reflect circularlypolarized light.

FIG. 6 show an illumination system 600 of a head-mounted display devicethat include similar components as illumination system 400 except that afirst polarization selective reflector 416 and a second polarizationselective reflector 426 are included instead of the first polarizationselective reflector 412 and the second polarization selective reflector422, and that the phase retarder 440 is not included.

In some embodiments, one or more light sources provide light 662 havinga polarization which may be represented as a combination of twocircularly polarized components (e.g., linearly polarized, ellipticallypolarized, or unpolarized).

Light having circular polarization states refers to light that has twoorthogonal constituent waves (e.g., a first constituent wave oscillatingin the y-z plane, and a second constituent wave oscillating in the x-zplane) having equal magnitude and a relative phase difference thatdiffers by multiples of 90°. In such cases, a scalar amplitude of thelight wave is constant but the electric-field vector of the light waverotates in either a clockwise (e.g., right-circularly polarized light)or counter-clockwise (e.g., left-circularly polarized light) manner.

In FIG. 6 , the light 662 include a first circular polarizationcomponent (e.g., right-circularly polarized component), and a secondcircular polarization component (e.g., left-circularly polarizedcomponent).

The light 662 is incident on the first polarization selective reflector416. In some embodiments, the first polarization selective reflector 416reflects a first portion (e.g., the portion that is right-circularlypolarized) of the light 662 as light 664, toward the spatial lightmodulator 452, and transmits a second portion (e.g., the portion that isleft-circularly polarized) of the light 662 as light 667. The spatiallight modulator 452 receives the light 664 and depending on the settingfor a particular location (e.g., pixel) of the spatial light modulator452, modifies the light 664 (or a portion of the light 664 that impingeson the particular location of the spatial light modulator 452), andprovides (e.g., reflects) light 682 having a polarization different fromthe polarization of the light 664 towards the first polarizationselective reflector 416. For example, the light 664, which isright-circularly polarized, is modified by the spatial light modulator452 to become light 682 that is left-circularly polarized. While In FIG.6 , the light 664 is shown offset from the light 682 along thez-direction for clarity, the light 682 reflects from the spatial lightmodulator 452 at or close to a location where the light 664 strikes thespatial light modulator 452. The left-circularly polarized light 682directed toward the first polarization selective reflector 416 istransmitted through the first polarization selective reflector 416 aslight 684, while maintaining its left-circular polarization. The light684 then enters the projection system 450.

As explained above, the first polarization selective reflector 416transmits the second portion (e.g., the portion that is left-circularlypolarized) of the light 662 as light 667, toward the second polarizationselective reflector 426. In some embodiments, the first polarizationselective reflector 416 and the second polarization selective reflector426 both reflect light having right-circular polarization and transmitlight having left-circular polarization. The left-circularly polarizedlight 667 is transmitted through the second polarization selectivereflector 426 and maintains its left-circular polarization as light 668.In some embodiments, the left-circularly polarized light 668 is incidenton the mirror 430 at a particular incident angle (e.g., at an incidentangle less than 10° or 5°, such as 0°).

The mirror 430 reflects (e.g., retroreflect) the circularly polarizedlight 668 toward the second polarization selective reflector 426 aslight 674. When the circularly polarized light 668 is reflected by themirror 430, a direction in which the electric field vector of thecircularly polarized light 668 rotates is reversed. Thus, the circularlypolarized light 674 reflected toward second polarization selectivereflector 426 has a handedness (e.g., right-circularly polarized light)opposite to the circularly polarized light 668 (e.g., left-circularlypolarized light). The second polarization selective reflector 426reflects the right-circularly polarized light 674 toward the spatiallight modulator 452 as light 676, while maintaining its right-circularpolarization.

The spatial light modulator 452 modifies a polarization of theright-circularly polarized light 676 to form light 678 that isleft-circularly polarized, and directs the light 678 toward the secondpolarization selective reflector 426. The left-circularly polarizedlight 678 is transmitted through the second polarization selectivereflector 426 as light 680, while maintaining its left-circularpolarization. The light 680, which is left-circularly polarized, thenenters the projection system 450.

Although the first polarization selective reflector 416 and the secondpolarization selective reflector 426 in FIG. 6 are described as capableof reflecting the right-circularly polarized light and transmitting theleft-circularly polarized light, in some embodiments, the firstpolarization selective reflector 416 and the second polarizationselective reflector 426 configured to reflect the left-circularlypolarized light and transmit the right-circularly polarized light areused.

Although FIGS. 4A, 4C, 5, and 6 illustrate illumination systems in whichboth the first polarization selective reflector and the secondpolarization selective reflector are configured to reflect light havinga first polarization and transmit light having a second polarizationdifferent from the first polarization, an illumination system may beconfigured with two polarization selective reflectors that areconfigured to reflect light having different polarizations (and transmitlight having different polarizations). Thus, in some embodiments, anillumination system includes (i) a first polarization selectivereflector configured (e.g., positioned and/or oriented) to reflect lighthaving a first polarization and transmit light having a secondpolarization and (ii) a second polarization selective reflectorconfigured (e.g., positioned and/or oriented) to reflect light havingthe second polarization and transmit light having the firstpolarization. For example, the first polarization selective reflectormay reflect light having horizontal polarization and transmit lighthaving vertical polarization and the second polarization selectivereflector may reflect light having vertical polarization and reflectlight having horizontal polarization. In another example, the firstpolarization selective reflector may reflect light having verticalpolarization and transmit light having horizontal polarization and thesecond polarization selective reflector may reflect light havinghorizontal polarization and reflect light having vertical polarization.In such embodiments, the illumination system includes a polarizationretarder (e.g., a half-wave plate). In some embodiments, thepolarization retarder is located between the first polarizationselective reflector and the second polarization selective reflector. Insome embodiments, the polarization retarder is located on the firstpolarization selective reflector or the second polarization selectivereflector (e.g., the polarization retarder is integrated with the firstpolarization selective reflector). In some embodiments, the polarizationretarder converts a vertically polarized light from the firstpolarization selective reflector to a horizontally polarized light, orvice versa.

FIGS. 7A-7C show a method 700 of forming a first polarization selectivereflector and a second polarization selective reflector into an integraloptical component.

In some embodiments, a prism 702 is used to form the integral opticalcomponent. In some embodiments, the prism 702 is a right-angle prism. Insome embodiments, the prism 702 has a base that has a shape of anisosceles triangle. In some embodiments, the prism 702 is a right-angleprism having a base that is an isosceles right-angle triangle. In someembodiments, the prism 702 is made of glass, including glasses with ahigh index of refraction. In some embodiments, the prism 702 is made ofpolymers, for example, polymers with a low birefringence. In someembodiments, glasses with a high index of refraction has an index ofrefraction greater than 1.52.

Suitable polymers include polydimethyl siloxane, polymethylmethacrylate,cyclic polyolefins, polymers made from oligomers, and other polymersthat can form optical components having low birefringence.

In some embodiments, a polarization selective film 704 is used to formthe integral optical component. In some embodiments, the polarizationselective film 704 is a wire grid polarizer film, a birefringent opticalfilm, a cholesteric polarization selective film, or any combinationthereof.

In some embodiments, the prism 702 and/or the polarization selectivefilm 704 are coated with an adhesive and/or a primer. In someembodiments, two lateral surfaces of the prism 702 are coated with anadhesive and/or a primer. In some embodiments, the primer is anundercoat that is a preparatory coating put on the prism 702 or thepolarization selective film 704. In some embodiments, priming allowsbetter adhesion to a surface of the prism 702. In some embodiments,priming allows better adhesion to a surface of the polarizationselective film 704. Better adhesion increases durability, and providesadditional protection for the prism 702 and/or the polarizationselective film 704. In some embodiments, the adhesive and the primer areoptically transparent (e.g., at least for visible light).

In some embodiments, the integral optical components includes a firstprism, and the first polarization selective reflector 710 is disposed ona first surface of the first prism 702 and the second polarizationselective reflector 720 is disposed on a second surface of the firstprism 702.

In some embodiments, a method of manufacturing the polarizationselective reflector includes bonding two polarizing beam splitterstogether with an adhesive. In some embodiments, the adhesive has asimilar refractive index to the prism 702 or the polarization selectivereflector film 704 over the wavelengths of interest. In someembodiments, the wavelengths of interest span between 350 nm to 900 nm.In some embodiments, the wavelengths of interest span one or moreshorter ranges at each of red, green, or blue (e.g., 564-580 nm for red;534-545 nm for green; and 420-440 nm for blue) spectra.

In some embodiments, instead of using adhesive or primer, thepolarization selective film 704 is simply conformed to the prism 702. Insome embodiments, conforming the film 704 includes slightly stretchingor heating the film 704, which allows some of the electrons on thesurface to be removed from the film 704, creating patches of positiveand negative electrostatic charge. When the film 704 is a goodinsulator, this charge persists for a sufficient period of time toinduce an opposite charge in the other surface (e.g., the prism 702) tocause the film 704 to conform to the prism 702.

After the film 704 and the prism 702 are joined adhesively orconformally such that the film 704 covers two surfaces of the prism 702,the first surface of the prism 702 serves as a first polarizationselective reflector 710, while the second surface of the prism 702serves as a second polarization selective reflector 720. The firstpolarization selective reflector 710 and the second polarizationselective reflector 720 define an angle 714 between them. In someembodiments, the angle 714 is a right angle.

FIG. 7C shows the prism 702 coupled with mating prisms 730 and 740. Insome embodiments, the mating prisms 730 and 740 are attached to thefirst polarization selective reflector 710 and the second polarizationselective reflector 720, respectively. In some embodiments, the matingprisms 730 and 740 are cast and cured using a suitable resin. Suitableresins include polymers with a low birefringence, such as, for example,polydimethyl siloxane, polymethylmethacrylate, cyclic polyolefins,polymers made from oligomers, and other polymers that form opticalcomponents having low birefringence. In some embodiments, the matingprims 730 and 740 integrated with polarization selective reflectors(e.g., the mating prism 730 is coupled with the first polarizationselective reflector 710 and the mating prism 740 is coupled with thesecond polarization selective reflector 720) are attached to the prism702 to form the integral optical component.

In some embodiments, a beam splitter assembly includes a second prism(e.g., a mating prism 740) and a third prism (e.g., a mating prism 730).The second prism is in contact with the second polarization selectivereflector (e.g., a second polarization selective reflector 720), and thethird prism is in contact with the first polarization selectivereflector (e.g., a first polarization selective reflector 710).

In some embodiments, a method of manufacturing a polarizing beamsplitter includes providing a prism with an isosceles right angletriangular profile (e.g., the prism 702), applying a reflectivepolarizer to the two isosceles angle faces (e.g., polarization selectivefilm 704), and immersing the prism into material to form anapproximately rectangular profile (e.g., molding a rectangular prismwith the embedded polarization selective reflectors 710 and 720).

FIG. 8A shows a plan view of an illumination system 800 in accordancewith some embodiments. In FIG. 8A, the illumination system 800 includeslight source 810, a tapered integrator 820, a first mirror 822, aFresnel reflector 830, a first polarization selective reflector 840 anda second polarization selective reflector 850. In some embodiments, theFresnel reflector includes a series of long, narrow, shallow-curvature(or even flat) mirrors to direct (e.g., focus, collimate) light towardthe first polarization selective reflector 840. In some embodiments, thefirst polarization selective reflector 840 is a polarizing beamsplitter. In some embodiments, the second polarization selectivereflector 850 is a polarizing beam splitter. In FIG. 8A, theillumination system 800 also includes the phase retarder 440 (when thelight source 80 emits light having planar polarization(s)) and themirror 430.

In some embodiments, light 812 emitted by the light source 810 ispartially collimated and homogenized by the tapered integrator 820. Thelight 812 reflects off the first mirror 822 at a wider end of thetapered integrator 820. In some embodiments, the first mirror 822includes a reflective coating disposed on a surface of the wider end ofthe tapered integrator 820. The light 812 reflects at the first mirror822 as light 814 and the light 814 is reflected again at a surface 832of the Fresnel reflector 830 as light 816. In some embodiments, thelight 814 makes a right angle with respect to the light 812. In someembodiments, the light 816 makes a right angle with respect to the light814 such that the light 816 propagates in a direction counter to apropagation direction of the light 812 (e.g., the light 816 isanti-parallel to the light 812). In some embodiments, the light 812, 814and 816 lie in the same y-z plane.

In some embodiments, the light source 810 has a divergence and emitslight 813 that is not parallel to the light 812 upon emission from thelight source 810. After reflecting off a side surface of the integrator820, the light 813 is substantially parallel to the light 812. Thus, theintegrator 820 collimates the light emitted from the light source 810.After the light 813 is reflected by the first mirror 822 as light 815,the light 815 is substantially parallel to the light 814. The light 815after reflecting off a surface 834 of the Fresnel reflector 830 becomeslight 817, which is substantially parallel to the light 816.

In some embodiments, the light 816 follows a similar optical path as thevertically polarized light 466 shown in FIG. 4A.

In some embodiments, light 825 follows the optical path of thevertically polarized light 494 or the light 486 described in FIG. 4B.The light 825 is directed back toward the light source 810 for recyclingof the illumination light. The intermediate paths of the light (e.g.,reflection of the light by the reflector 430, the first polarizationselective reflector 840, or the second polarization selective reflector850, before the light is directed as light 825) are not shown in FIG. 8Aso as not to obscure other aspects of the illumination system 800.

In some embodiments, the illumination system 800 is optically coupledwith the spatial light modulator 452 (not shown in FIG. 8A). When theillumination system 800 is optically coupled with the spatial lightmodulator 452, the spatial light modulator 452 may be positioned to lieon a y-z plane below the plane of the drawing of FIG. 8A, as shown in,for example, FIG. 4A.

In some embodiments, the first polarization selective reflector 840 andthe second polarization selective reflector 850 are not disposed on thesame right-angle prism as shown in FIG. 7B. Instead, the firstpolarization selective reflector 840 is disposed on a first prism (e.g.,mating prism 730 of FIG. 7C) and the second polarization selectivereflector 850 is disposed on a second prism (e.g., mating prism 740 ofFIG. 7C) that is separate from the first prism.

In some embodiments, the light not reflected by the first polarizationselective reflector 840 toward the spatial light modulator (e.g., thelight 466 in FIG. 4A that is transmitted toward the second polarizationselective reflector 420) will propagate in free space instead of througha prism (e.g., prism 702 in FIG. 7B). In some embodiments, light that isreflected by the first polarization selective reflector 840 travelsthrough the first prism (e.g., mating prism 730) before it illuminatesthe spatial light modulator 452.

FIG. 8B shows the illumination system 800 in a perspective view. Thelight source 810 emits the light 812, which propagates through thetapered integrator 820. The light 812 reflects off the first mirror 822as light 814. The light 814 is reflected again at the surface 832 of theFresnel reflector 830 as the light 816.

In some embodiments, the light 816 includes two orthogonal planarpolarization components (e.g., vertically polarized light andhorizontally polarized light). The first polarization selectivereflector 840 transmits vertically polarized light 818 toward the secondpolarization selective reflector 850, and reflects horizontallypolarized light 821 along the −x direction, toward a spatial lightmodulator (not shown).

The vertically polarized light 818 transmits through the secondpolarization selective reflector 850, and impinges on the phase retarder440, which is a quarter-wave plate configured to convert the linearly(e.g., vertically) polarized light 818 to circularly polarized light(e.g., left-circularly polarized light) and transmit the circularlypolarized light toward the mirror 430. The mirror 430 reflects thecircularly polarized light and reverses the handedness of the circularlypolarized light. As the circularly polarized light passes through thephase retarder 440, the phase retarder 440 converts the circularlypolarized light to linearly polarized light 823 and transmit thelinearly polarized light 823 toward the second polarization selectivereflector 850. In some embodiments, a plane of vibration of the linearlypolarized light 823 (e.g., horizontally polarization) is perpendicularto a plane of vibration of the linearly polarized light 818 (e.g.,vertically polarization), and the second polarization selectivereflector 850 reflects the linearly polarized light 823 toward thespatial light modulator (not shown), along the −x direction as light824.

In some embodiments, as shown in FIG. 9 , an illumination system 900includes two light sources 810 and 910. Light 912 emitted by the lightsource 910 follows a similar path as the light 812 emitted by the lightsource 810. The light 912 enters a second integrator 920, reflects off asecond Fresnel reflector 930 and is first incident on the secondpolarization selective reflector 850, instead of the first polarizationselective reflector 840. This configuration eliminates the need for areflector and a phase retarder shown in FIG. 8A.

In some embodiments, directional backlights or other means providesuitable illumination to the first polarization selective reflector 840and the second polarization selective reflector 850. In someembodiments, the light sources emit polarized light (e.g., the lightsource is a laser configured to provide a polarized light). In someembodiments, the light sources emit unpolarized light, and light havinga polarization that is transmitted by the two polarization selectivereflectors is recycled by the opposing light source. In someembodiments, a reflective or absorbing polarizer is placed in the pathof the light between the light sources and the first or secondpolarization selective reflector to modify the polarization of thelight. In some embodiments, additional mirror coatings and optionalquarter wave retarders are used, which may further increase anefficiency of the system 900.

In some embodiments, at least 25% of light reflected by the spatiallight modulator 452 (e.g., LCoS) is recycled by the illumination system.

FIG. 10A shows a system 1000 in accordance with some embodiments. Thesystem 1000 includes light source 1002. In some embodiments, the lightsource 1002 emits light having two orthogonal polarization components.In some embodiments, the light source 1002 emits unpolarized light. Insome embodiments, the light source is an LED. Light 1022 represents anexample ray having horizontal polarization, and light 1020 represents anexample ray having vertical polarization. In FIG. 10A, the light 1020and 1022 are illustrated as traveling in different directions from thelight source 1002 for clarity. The light 1020 and the light 1022 passthrough a lens 1004 that collimates and/or homogenizes the light. Boththe light 1020 and the light 1022 impinge upon a first polarizationselective reflector 1006. In some embodiments, the first polarizationselective reflector 1006 selectively reflects the horizontally polarizedlight toward a spatial light modulator 1012, while the verticallypolarized light 1020 is transmitted through the first polarizationselective reflector 1006 toward a second polarization selectivereflector 1008. A mirror and quarter-wave plate combination 1010receives the light 1020 from the second polarization selective reflector1008 and reflects a horizontally polarized light back toward the secondpolarization selective reflector 1008. The second polarization selectivereflector 1008 reflects the horizontally polarized light toward thespatial light modulator 1012.

FIG. 10B shows a system 1030. The system 1030 includes light source 1032and light guide 1034. In some embodiments, the light guide 1034 has asmall size, which enables a compact illumination system. The light guide1034 has a number of extraction features 1036. The extraction features1036 allow portions of light propagating within the light guide 1034 toexit the light guide 1034. In some embodiments, the light guide 1034provides directional illumination to match an imaging F-number of aprojector (e.g., projection system 450).

The light source 1032, edge-coupled to the light guide 1034, emits light1040, which is guided (e.g., via total internal reflection) along thelight guide 1034. In some embodiments, the light source 1032 is an LEDlight source. In some embodiments, when the light 1040 impinges on oneof the extraction features 1036, the extraction feature steers the light1040 as light 1042 so that the light 1042 exits the light guide 1034(e.g., the light 1042 does not meet the total internal reflectioncondition on an opposite surface of the light guide 1034 and leaves thelight guide 1034 to impinge on the first polarization selectivereflector 1006). The illumination is directional and is tuned by theshape of the extraction features. In some embodiments, other directionallight guide are used, for example, a light guide with shallow prismextractors, where the light leaks out at grazing incident angles. Insome embodiments, the shallow prism extractors are combined with aturning film to provide a directional and uniform illumination. In someembodiments, the light 1042 follows a path that is similar to that ofeither light 1022 or light 1020 (depending on the polarization of thelight 1042), described with respect to FIG. 10A.

Many illumination configurations are compatible with the system 1030. Insome embodiments, the system 1030 having the “split prism” configurationwith the first polarization selective reflector 1006 and the secondpolarization selective reflector 1008 is coupled with the traditionalfly's eye homogenizer illumination. In some embodiments, an LED array isused in conjunction with a taper array or a microlenslet array.

Hereinafter, a “split prism” configuration refers to (e.g., V-shaped)arrangements of the first polarization selective reflector and thesecond polarization selective reflectors, for example, as shown in FIGS.4A-10B.

In some embodiments, the polarization selective reflectors in the “splitprism” arrangements described in FIGS. 4A-10B, are polarization volumeholograms instead of reflective polarizers. For example, in someembodiments, a first PVH is positioned in a first orientation, and asecond PVH is positioned in a second orientation non-parallel to thefirst orientation, and adjacent to the first polarization selectivereflector.

FIG. 11A is a schematic diagram illustrating a projection system inaccordance with some embodiments.

In FIG. 11A, a projection system 1100 receives illumination light fromone or more light sources (similar to light source 810, not shown inFIG. 11A). The projection system 1100 includes a first polarizationselective reflector 1110, a projection lens 1130, a phase retarder 1132disposed on a first surface of the projection lens 1130 (e.g., thesurface closer to the spatial light modulator 1152 than an opposing,second surface of the projection lens 1130), a reflective coating 1134disposed on the second surface of the projection lens 1130 (e.g., thesurface further from the spatial light modulator 1152 than the firstsurface). In some embodiments, the projection system 1100 is opticallycoupled to a spatial light modulator (SLM) 1152 for transmitting lightfrom the spatial light modulator. In FIG. 11A, the projection system1100 is also configured to illuminate the spatial light modulator 1152.In some embodiments, the projection system 1100 also includes an optics1140 (e.g., one or more lenses) that directs light to a waveguide (notshown) used for coupling light output from the projection system 1100into an eyebox of a user. In some embodiments, the optics 1140 is absentfrom the projection system 1100. In some embodiments, the projectionsystem 1100 includes a cover glass 1120. In some embodiments, the coverglass 1120 is located between the first polarization selective reflector1110 and the spatial light modulator 1152. In some embodiments, thecover glass 1120 is absent from the projection system 1100.

In some embodiments, the first polarization selective reflector 1110 isdisposed along a diagonal of a beam splitter assembly 1116. The beamsplitter assembly 1116 includes a first prism 1112 and a second prism1114. In some embodiments, the first prism 1112 is a right-angle prismhaving a hypotenuse (or a slope facet). In some embodiments, the secondprism 1114 is a right-angle prism having a hypotenuse (or a slopefacet). In some embodiments, the first polarization selective reflector1110 is disposed between the first prism 1112 and the second prism 1114,parallel to the hypotenuse (or the slope facet) of the first prism 1112and the hypotenuse (or the slope facet) of the second prism 1114. Insome embodiments, the first polarization selective reflector 1110 is incontact with the slope facet of the first prism 1112 and the slope facetof the second prism 1114.

In some embodiments, the projection system 1100 includes one or morepolarization filtering elements. In some embodiments, at least onepolarization filtering element is located between the first polarizationselective reflector 1110 and the one or more light sources (e.g.,adjacent to a surface of the beam splitter assembly 1116 away from theoptics 1140) for reducing transmission of light (or a component thereof)having a particular polarization (e.g., the projection system 1100 isconfigured to operate with a vertically polarized light as an input, apolarization filtering element is used to reduce transmission of ahorizontally polarized light into the beam splitter assembly 1116). Insome embodiments, at least one polarization filtering element is locatedbetween the beam splitter assembly 1116 and the optics 1140 for reducingtransmission of light having a particular polarization (e.g., when theprojection system 1100 is configured to provide light having a verticalpolarization, a polarization filtering element is used to reducetransmission of a horizontally polarized light output from the beamsplitter assembly 1116). In some embodiments, the polarization filteringelement is a polarization selective reflector configured to reflectlight having a first polarization (e.g., undesired horizontalpolarization) orthogonal to a second polarization (e.g., desiredvertical polarization), and transmit light of the second polarization.

In some embodiments, one or more light sources provide light 1162 havinga single polarization state. In some embodiments, the singlepolarization state is a planar polarization state. In some embodiments,the light 1162 is vertically polarized and the first polarizationselective reflector 1110 is configured to reflect vertically polarizedlight. The first polarization selective reflector 1110 reflects at leasta portion of the light 1162 as light 1164, toward the spatial lightmodulator 1152, while the light 1164 maintains its verticalpolarization. In some embodiments, in which the projection system 1100includes the cover glass 1120, the light 1164 passes through the coverglass 1120 before impinging on the spatial light modulator 1152.

The spatial light modulator 1152 receives the light 1164, and dependingon a setting for a particular location (e.g., pixel) of the spatiallight modulator 1152, modifies the light 1164 (or a portion of the light1164 that impinges on the particular location of the spatial lightmodulator 1152), and provides (e.g., reflects) the modified light aslight 1166 having a polarization (e.g., horizontally polarization)different from the polarization (e.g., vertically polarization) of thelight 1164 towards the first polarization selective reflector 1110.

In some embodiments, the light 1166 is horizontally polarized. The firstpolarization selective reflector 1110 directs the horizontally polarizedlight 1166 (e.g., transmits the horizontally polarized light 1166)toward the projection lens 1130. The phase retarder 1132 modifies thepolarization of the light 1166. For example, in configurations, in whichthe phase retarder 1132 is a quarter-wave plate, the quarter-wave plateturns the light 1166 into circularly polarized light 1168 and transmitthe light 1168 toward the reflective coating 1134. The reflectivecoating 1134 reflects the circularly polarized light 1168 toward thephase retarder 1132 as circularly polarized light 1170. When thecircularly polarized light 1168 is reflected by the reflective coating1134, a direction in which the electric field vector of the circularlypolarized light 1168 rotates is reversed. Thus, the circularly polarizedlight 1170 reflected toward the phase retarder 1132 has a handedness(e.g., left-circularly polarized light) opposite to the circularlypolarized light 1168 (e.g., right-circularly polarized light). As thecircularly polarized light 1170 passes through the phase retarder 1132,the phase retarder 1132 converts the circularly polarized light 1170 tolinearly polarized light 1172 and transmits it toward the firstpolarization selective reflector 1110. In some embodiments, a plane ofvibration of the linearly polarized light 1172 (e.g., verticallypolarized) is perpendicular to a plane of vibration of the linearlypolarized light 1166 (e.g., horizontally polarized), and the firstpolarization selective reflector 1110 reflects the linearly polarizedlight 1172 toward the optics 1140 as light 1174.

In some embodiments, the projection lens 1130 has an optical power(e.g., at least one of the first surface and the second surface of theprojection lens 1130 is curved). For example, at least one of the firstsurface and the second surface of the projection lens 1130 may be aconvex surface. Additionally or alternatively, at least one of the firstsurface and the second surface of the projection lens 1130 may be aconcave surface. In some embodiments, the projection lens 1130 projectsthe light from the spatial light modulator 1152 to form an image at animage plane. In some embodiments, the projection lens 1130 has nooptical power (e.g., the projection lens 1130 is replaced with a flatsubstrate).

FIG. 11B is a schematic diagram illustrating a projection system 1102 inaccordance with some embodiments. The projection system 1102 is similarto the projection system 1100 except that, in the projection system1102, the spatial light modulator 1152 and the reflective coating 1134are not located on opposite sides of a beam splitter assembly, whereas,in the projection system 1100, the spatial light modulator 1152 and thereflective coating 1134 are located on opposite sides of the beamsplitter assembly 1116.

The projection system 1102 receives illumination light 1163 from one ormore light sources (not shown). The projection system 1102 is arrangedso that a first polarization selective reflector 113 directs the light1163 (e.g., transmits the light 1163) to the spatial light modulator1152 (through the cover glass 1120 if the cover glass 1120 is includedin the projection system 1102). In some embodiments, the firstpolarization selective reflector 1113 is disposed along a diagonal of abeam splitter assembly 1117.

In some embodiments, the one or more light sources provide the light1163 having a single polarization state. In some embodiments, the light1163 has a single planar polarization state (e.g., linear polarization).In some embodiments, the light 1163 is vertically polarized and thefirst polarization selective reflector 1113 is configured to transmitvertically polarized light toward the spatial light modulator 1152. Insome embodiments with the cover glass 1120, the light 1163 passesthrough the cover glass 1120 before impinging on the spatial lightmodulator 1152.

The spatial light modulator 1152 receives the light 1163, and dependingon a setting for a particular location (e.g., pixel) of the spatiallight modulator, modifies the light 1163 (or a portion of the light1163), and provides (e.g., reflects) the modified light as light 1165having a polarization (e.g., horizontal polarization) different from thepolarization (e.g., vertical polarization) of the light 1163 toward thefirst polarization selective reflector 1113.

The first polarization selective reflector 1113 reflects at least aportion of the horizontally polarized light 1165 as horizontallypolarized light 1167 and directs the light 1167 toward the projectionlens 1130. The phase retarder 1132, which is a quarter-wave plate insome embodiments, turns the light 1167 into circularly polarized light1169 and transmits the circularly polarized light 1169 toward thereflective coating 1134. The reflective coating 1134 reflects thecircularly polarized light 1169 toward the phase retarder 1132 ascircularly polarized light 1171. When the circularly polarized light1169 is reflected by the reflective coating 1134, a direction in whichthe electric field vector of the circularly polarized light 1169 rotatesis reversed. Thus, the circularly polarized light 1171 reflected towardthe phase retarder 1132 has a handedness (e.g., right-circularpolarization) opposite to the circularly polarized light 1169 (e.g.,left-circular polarization). As the circularly polarized light 1171passes through the phase retarder 1132, the phase retarder 1132 convertsthe circularly polarized light 1171 to linearly polarized light 1173 andtransmits linearly polarized light 1173 toward the first polarizationselective reflector 1113. In some embodiments, a plane of vibration ofthe linearly polarized light 1173 (e.g., vertically polarized) isperpendicular to a plane of vibration of the linearly polarized light1167 (e.g., horizontally polarized), and the first polarizationselective reflector 1113 transmits the linearly polarized light 1173toward the optional optics 1140.

The projection systems shown in FIGS. 11A and 11B utilize a foldedoptical path for the light from the spatial light modulator 1152, whicheliminates the need for a long straight path for projecting the lightfrom the spatial light modulator and enables a compact projectionsystem, compared to a projection system that does not utilize a foldedoptical path. In addition, the beam splitter assembly facilitatesilluminating the spatial light modulator at a normal incident angle (ora near normal incident angle) and collecting light from the spatiallight modulator at a normal collection angle (or a near normalcollection angle), which improves the image quality.

Although FIGS. 11A and 11B show that the projection lens 1130 has thephase retarder 1132 disposed on the first surface of the projection lens1130 and the reflective coating 1134 disposed on the second surface ofthe projection lens 1130, in some embodiments, at least one of the phaseretarder 1132 and the reflective coating 1134 is separate from theprojection lens 1130. For example, the phase retarder 1132 and thereflective coating 1134 separate from the projection lens 1130 may beused instead of a single integrated projection lens with the phaseretarder 1132 and the reflective coating 1134.

FIG. 12 is a schematic diagram illustrating a projection system 1200 inaccordance with some embodiments. The projection system 1200 is similarto the projection system 1100, except that the projection system 1200 isoptically coupled with a waveguide 1142.

In some embodiments, the projection system 1200 receives illuminationlight 1210 from one or more light sources (not shown). In someembodiments, the projection system 1200 is used in conjunction withvarious types of spatial light modulators (SLM). In some embodiments,the spatial light modulator is a Liquid Crystal on Silicon (LCoS), andin such cases, the projection system 1200 is called an LCoS projectionsystem. A spatial light modulator 1152 (e.g., LCoS) reflects theillumination light based on a setting for a pixel where the illuminationlight 1210 impinges on the LCoS.

FIG. 12 shows rays from the spatial light modulator 1152. In FIG. 12 ,for each of the three different pixels 1212, 1214, and 1216 on thespatial light modulator 1152, three rays are illustrated as examples.

FIG. 12 shows a first ray 1218-1, a second ray 1218-2, and a third ray1218-3 from pixel 1216. The first ray 1218-1 makes an angle 1218-1 awith respect to the second ray 1218-2, and the third ray 1218-3 makes anangle 1218-3 a with respect to the second ray 1218-2. The rays 1218-1,1218-2, and 1218-13 are first reflected by the reflective coating 1134on a second surface of the projection lens 1130, and then reflected bythe first polarization selective reflector 1110 before impinging on thewaveguide 1242. FIG. 12 also shows three rays, 1220-1, 1220-2, and1220-3 from pixel 1212. The ray 1220-3 makes an angle 1220-3 a relativeto the ray 1220-2. The rays 1220-1, 1220-2, and 1220-3 are reflected bythe reflective coating 1134 on the second surface of the projection lens1130, and then reflected by the first polarization selective reflector1110 before impinging on the waveguide 1242. Similarly, rays from pixel1214 also are reflected by the reflective coating 1134 on the secondsurface of the projection lens 1130, and then reflected by the firstpolarization selective reflector 1110 before impinging on the waveguide1242.

In FIG. 12 , both the ray 1218-3 from pixel 1216 and the ray 1220-3 frompixel 1212 impinge at location 1244 of the waveguide 1242, and both theray 1218-1 from pixel 1216 and the ray 1220-1 from pixel 1212 impinge onlocation 1248 of the waveguide 1242. Similarly, middle rays (e.g.,1218-2, 1220-2) from each of the three pixels 1212, 1214, and 1216impinge at location 1246 of the waveguide 1242.

In some embodiments, a magnitude of the angle 1218-3 a equals amagnitude of the angle 1220-3 a. The location 1244 on the waveguide 1242receives rays from different pixels (e.g., pixel 1212 and pixel 1216)that reflect off the spatial light modulator 1152 (e.g., LCoS) at thesame angle.

Rays reflecting from different pixels are relayed by the projection lens1130 to the same location on the waveguide 1242. In some embodiments,both the spatial light modulator 1152 and the waveguide 1242 are locatedat an optical path length that corresponds to a focal length of theprojection lens 1130. This allows the projection lens 1130 to provideFourier transforming effect on the received light. For, angularinformation at the spatial light modulator 1152 is converted intopositional information on the waveguide 1242 by the projection lens1130.

In FIG. 12 , a dimension of the projection system 1200, including thespatial light modulator 1152 (e.g., LCoS) and the projection lens 1130,along the y-direction is marked by a double-headed arrow 1230. In someembodiments, the dimension represented by the arrow 1230 is between 4 mmto 15 mm (e.g., the dimension is 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14,or 15 mm).

In some embodiments, a field of view of the projection system isdifferent along two orthogonal directions (e.g., the x direction and thez direction).

FIG. 13A shows another way of reducing a volume of a projection systemin accordance to some embodiments. The projection system 1300 uses afirst prism 1312 that has a different size and a different shapecompared to a second prism 1314. In some embodiments, a cross-sectionalong the y-z plane of the second prism 1314 is a right trapezoid, whilea cross-section along the y-z plane of the first prism 1312 remains aright angle prism. In some embodiments, the first prism 1312 is a rightangle prism having a first side 1316 a, a second side 1316 b, and ahypotenuse 1316 c, where the first side 1316 a makes a right angle withthe second side 1316 b. In some embodiments, the second prism 1314 is aright trapezoid having a first side 1318 a, a second side 1318 b, athird side 1318 c, and a fourth side 1318 d. In some embodiments, thefourth side 1318 d of the second prism 1314 has the same length as thehypotenuse 1316 c of the first prism 1312.

In some embodiments, a region 1260 of the second prism 1114 in FIG. 12is not used optically (e.g., no illumination light 1210 reflected by thespatial light modulator 1152 traverses the region 1260). As a result, insome embodiments, the first prism 1312 and the second prism 1314 areformed by truncating the first prism 1112 and the second prism 1114along a line 1262. The projection system 1300 in such embodiments has asimilar field of view compared to the embodiments shown in FIG. 12 ,while a volume of the projection system 1300 is significantly smaller(e.g., 30%, 40%, 50%, 60%, 70%, smaller) than the volume of theprojection system 1200.

In some embodiments, an angular range 1340 describes a spread of anangle of a field of view provided by three pixels 1350, 1352, and 1354on the spatial light modulator 1152 when a beam splitter with twoidentical prisms, similar to the beam splitter shown in FIG. 12 , isused. By using two prisms of different sizes (e.g., the first prism 1312and the second prism 1314), the field of field increases by an angularrange 1342, a spread of an angle of a field of view provided by anadditional pixel 1356 relative to the pixel 1350. In some embodiments,the angular range 1340 is between 20 degrees to 40 degrees (e.g., valueof the angular range 1340 is 20, 25, 30, 35, or 40 degrees). In someembodiments, the angular range 1342 is between 5 degrees to 20 degrees(e.g., value of the angular range 1342 is 5, 10, 15, or 20 degrees). Allthree rays originating from the pixel 1356 are received by optics in theprojection system 1300 (e.g., the second prism 1314, the projection lens1130).

In some embodiments, a corner 1360 of the projection system 1300 is onlyminimally traversed (if at all) by any optical light. Thus, the corner1360 need not be strictly right angle, some deviations from being rightangle is more acceptable at the corner 1360, than at a corner formed bythe side 1318 b and the side 1318 c.

In some embodiments, a value D2 of a width of the projection system 1300is between 2 mm to 15 mm (e.g., the value D2 is 4, 5, 6, 7, 8, 9, 10,11, 12, 13, 14, or 15 mm).

In some embodiments, the projection lens 1130 is rotationally symmetric.

A middle ray from each of the four pixels 1350, 1352, 1354, 1356 impingeat location 1362 of a waveguide (not shown). A right ray (e.g., the rayin each bundle of light emitting from a particular pixel that has thesmallest z value at the projection lens 1130) from each of the fourpixels 1350, 1352, 1354, 1356 impinge at location 1364 of the waveguide(not shown). A left ray (the ray in each bundle of light emitting from aparticular pixel that has the largest z value at the projection lens1130) from each of the four pixels 1350, 1352, 1354, 1356 impinge atlocation 1361 of the waveguide (not shown).

FIG. 13B shows side views and top views of the beam splitter assembly ofFIG. 12 (left) and the beam splitter assembly 1301 of FIG. 13A (right).

A light emitter has a size and spread. Etendue is a product of an areaof the light emitter and the solid angle of the light beam, anddescribes the size and angular spread of a beam of light as it passesthrough an optical system. The larger the beam angle or the larger thesource size, the larger the etendue. Etendue is the optical equivalentof entropy: etendue of a light beam does not decrease as it passesthrough an optical system. For example, losses due to scatteringincrease the etendue; more useful light energy has a smaller etenduevalue.

Systems that illuminate spatial light modulators perform better whenlight having uniform and low etendue illuminates the spatial lightmodulator. Providing such uniform and low etendue illumination commonlyinvolves large optical components that can add substantial weight andvolume.

FIG. 14A shows a compact spatial light modulator with illuminationsystem 1400 having a light source 1402. The illumination system 1400uses a polarizing beam splitter 1412 to provide an extended illuminationpath. In some embodiments, the light source 1402 is a light emitteddiode (LED), a SLED (superluminescent LED), a RCLED (resonate cavityLED), a laser diode, or a wavelength conversion device. An example of awavelength conversion device is a quantum dot or quantum well emittercombined with a pump light source. In some embodiments, the illuminationsystem 1400 includes an integrator rod 1404, which partially collimatesand homogenizes light emitted by the light source 1402. In someembodiments, a lens system or a combination of a lens and an integratorrod partially collimates light emitted by the light source 1402. In someembodiments, a tapered optical fiber or an array of tapered opticalfibers at least partially collimates light emitted by the light source1402.

In some embodiments, the illumination system 1400 includes a singlesource. In some embodiments, the illumination system 1400 includes alinear array of sources. In some embodiments, the illumination system1400 includes a two-dimensional array of sources. In some embodiments,the light sources are selectively powered to provide zonal illumination.Zonal illumination is a spatially selective way of illuminating one ormore regions (or zones) of a target area (e.g., a spatial lightmodulator 1430).

In some embodiments, the illumination system 1400 includes a divertingoptic 1406. The diverting optic 1406 is used to reduce a footprint ofthe illumination system 1400. In some embodiments, the diverting optic1406 is a prism configured to divert an incoming beam of light 1420 bysome angle (e.g., by 90 degree from the light 1420 travelingsubstantially along the x-direction to light 1422 travelingsubstantially along the −z direction). In some cases, light delivered tothe polarizing beam splitter 1412 is polarized. In some embodiments, anabsorbing polarizer is used to polarize the light delivered to thepolarizing beam splitter 1412. In some embodiments, a polarizationselective reflector is used, and the polarization selective reflectorreflects a light component having a particular polarization back to thelight source 1402. In some configurations, the light component havingthe particular polarization is recycled. In some embodiments, apolarization converter is used to polarize the light. In someembodiments, a combination of one or more of an absorbing polarizer, apolarization selective reflector, or a polarization converter is used.The light is polarized at any position between the light source 1402 andthe polarizing beam splitter 1412.

The light 1422 passes through an aperture 1410 of a mirror 1408 andquarter-wave plate 1409 (e.g., a common aperture that extends throughboth mirror 1408 and quarter-wave plate 1409), and enters the polarizingbeam splitter 1412. In some embodiments, the illumination system 1400includes a single mirror 1408 and a single quarter-wave plate 1409, eventhough each element (e.g., mirror 1408 or quarter-wave plate 1409) isshown in FIG. 14 as two separate pieces due to the presence of theaperture 1410. In some embodiments, the mirror 1408 and the quarter-waveplate 1409 are integrally formed.

A polarization selective reflector 1414 receives the light 1422 anddirects the light 1422 (depending on its polarization) toward apolarization selective reflector 1416. In some embodiments, directingthe light 1422 includes transmitting the light 1422 through thepolarization selective reflector 1414. The polarization selectivereflector 1416 reflects the light 1422 as light 1424 and directs thelight 1424 toward the polarization selective reflector 1414. Thepolarization selective reflector 1414 directs the light 1424 (dependingon its polarization) toward the mirror 1408 and the quarter-wave plate1409.

The quarter-wave plate 1409 is adjacent to the mirror 1408. Thecombination of the quarter-wave plate 1409 and the mirror 1408 receivesthe light 1424 and reflects the light 1424 as light 1426. Thequarter-wave plate 1409 causes light 1426 (e.g., the reflected light) tohave a polarization state orthogonal to the light 1424 (e.g., the light1424 has a first polarization state before impinging on the quarter-waveplate 1409, and the light 1426 has a second polarization state,orthogonal to the first polarization state, after passing through thequarter-wave plate 1409; the light 1424 is horizontally polarized, andthe light 1426 is vertically polarized; or the light 1424 is verticallypolarized, and the light 1426 is horizontally polarized). In someembodiments, the top surface of the beam splitter 1412 is coupled withan anti-reflection coating to reduce optical losses when the light 1424leaves the beam splitter 1412. Additionally or alternatively, in somecases, the light 1424 strikes the top surface of the beam splitter 1412at an incident angle that is close to zero so that the reflection by thetop surface of the beam splitter 1412 is reduced. In some embodiments,the mirror 1408 and/or an adjacent optical material have/has apreselected degree of scattering or randomization of a path of the light1424. For example, in some embodiments, the mirror 1408 has a finestructure that scatters light. In some embodiments, the mirror 1408causes controlled distortions of a path of the light 1424 (e.g., themirror 1408 has a non-flat surface, such as a curved surface). In someembodiments, a combination of both a fine structure and/or controlleddistortions are used. In some embodiments, scattering or distorting thelight 1424 does not substantially depolarize it. In some embodiments,the mirror 1408 has an aspherical shape, where one of the parametersused to optimize and create the aspherical shape is an illuminationuniformity at the spatial light modulator (e.g., the aspherical shapeimproves uniformity of the light provided to the spatial lightmodulator).

In some embodiments, the mirror 1408 has a number of aperturesdistributed over a region of the mirror 1408.

Due to the light 1426 having a polarization state orthogonal to apolarization state of the light 1424, the light 1426, instead of beingtransmitted through the polarization selective reflector 1414, isreflected by the polarization selective reflector 1414 and directedtoward a spatial light modulator (SLM) 1430 as light 1428. In someembodiments, the illumination system 1400 includes a SLM window 1418(between the beam splitter 1412 and the spatial light modulator 1430).In some embodiments, the light 1428 transmits through the SLM window1418 and impinges upon the spatial light modulator 1430. The spatiallight modulator 1430 spatially modulates the light 1428. In someembodiments, the spatial light modulator 1430 is an LCoS orferroelectric liquid crystal on silicon (FLCoS) imager that modulates apolarization state of light on individual pixels resolution. In someembodiments, the spatial light modulator 1430 includes a micro electromechanical system (MEMS) that is combined with a quarter-wave plate suchthat light impinging on a selected pixel (e.g., when the pixel isswitched on) is converted to an orthogonal polarization state. Theremaining ray paths and components are similar to the descriptionrelated to FIG. 11A (e.g., light 1432 is similar to light 1166; light1434 is similar to light 1172; light 1436 is similar to light 1174; lens1440 is similar to the projection lens 1130). In some embodiments, theillumination system 1400 includes optics 1442, which is similar tooptics 1140 shown in FIG. 11A.

As explained above with respect to FIGS. 11A and 11B, the illuminationsystem 1400 maybe configured so that the polarization selectivereflector 1414 transmits light entering the beam splitter 1412 (as shownin FIG. 14A) or reflects the light entering the beam splitter 1412.Examples of these are described with respect to FIGS. 14B-14E.

FIG. 14B shows a polarizing beam splitter 1450 having a cube 1452 thatcontains a first polarization selective reflector 1454. In someembodiments, the cube 1452 is composed of a first right-angle prism 1496and a second right-angle prism 1498. The cube 1452 has a first side 1453a, a second side 1453 b, a third side 1453 c, and a fourth side 1453 d.A second polarization selective reflector 1456 is adjacent to the cube1452, parallel and closest to the third side 1453 c of the cube 1452.For the polarizing beam splitter 1450, a surface where light enters(e.g., the first side 1453 a) is substantially parallel to the secondpolarization selective reflector 1456. In some embodiments, the firstpolarization selective reflector 1454 reflects light having a firstpolarization (e.g., vertically polarized) and the second polarizationselective reflector 1456 reflects light having a second polarizationdifferent from the first polarization (e.g., horizontally polarized).

A polarization of light blocked by the first polarization selectivereflector 1454 is orthogonal to a polarization of the light blocked (orreflected) by the second polarization selective reflector 1456. Forexample, in some embodiments, transmission axes of the firstpolarization selective reflector 1454 and the second polarizationselective reflector 1456 are configured such that polarized light 1462that enters the cube 1452 is transmitted through the first polarizationselective reflector 1454, and is reflected by the second polarizationselective reflector 1456. Such an orientation of transmission axes istermed “orthogonal polarization axes”, which refers to a configurationwhere a first polarizer transmits light with a first polarization state,and a second polarizer substantially blocks (or reflects) light with thefirst polarization state. Orthogonal polarization axes are possible forboth linear and circular polarizers.

In some embodiments, a second polarization selective reflector (e.g.,1456) is disposed on a first surface (e.g., third side 1453 c) of thefirst prism (e.g., second prism 1498), and light (e.g., 1462) enters theoptical device at a second surface (e.g., first side 1453 a) parallel tothe first surface (e.g., third side 1453 c).

FIG. 14C shows a polarizing beam splitter 1451 having a cube 1455 thatcontains a first polarization selective reflector 1458. In someembodiments, the cube 1455 is composed of a first right-angle prism 1492and a second right-angle prism 1494. The cube 1455 has a first side 1457a, a second side 1457 b, a third side 1457 c, and a fourth side 1457 d.The second polarization selective reflector 1456 is adjacent to the cube1455, parallel and closest to the fourth side 1457 d of the cube 1455.For the polarizing beam splitter 1451, a surface where light enters(e.g., the first side 1457 a) is substantially perpendicular to thesecond polarization selective reflector 1456. In some embodiments, boththe first polarization selective reflector 1454 and the secondpolarization selective reflector 1456 reflect light having the firstpolarization.

A polarization of light blocked (or reflected) by the first polarizationselective reflector 1458 is parallel to a polarization of the lightblocked (or reflected) by the second polarization selective reflector1456. For example, in some embodiments, transmission axes of the firstpolarization selective reflector 1458 and the second polarizationselective reflector 1456 are configured such that polarized light 1464that enters the polarizing beam splitter 1451 is reflected both by thefirst polarization selective reflector 1458 and the second polarizationselective reflector 1456.

In some embodiments, the second polarization selective reflector 1456 isdisposed on a first surface (e.g., fourth side 1457 d) of the firstprism (e.g., first prism 1492), and light enters the first prism at asecond surface (e.g., first side 1457 a) perpendicular to the firstsurface.

As shown above, an illumination system described herein can beconfigured to transmit light entering a beam splitter (as shown in FIG.14B) or reflect the light entering the beam splitter (as shown in FIG.14C). For brevity, not all possible configurations are illustrated, buta person having ordinary skill in the art would understand that oneconfiguration (e.g., the configuration shown in FIG. 14B) can be used inplace of the other configuration (e.g., the configuration shown in FIG.14C), or vice versa.

Illumination systems illustrated in FIGS. 14D and 14E are similar to theillumination systems illustrated in FIGS. 14B and 14C except that theillumination systems illustrated in FIGS. 14D and 14E include acombination of a mirror 1408 and a phase retarder (e.g., a quarter waveplate 1409) to further extend the optical path.

FIG. 14D shows an illumination system 1470. Light 1472 passes through anaperture 1410 in the mirror 1408 (and the quarter-wave plate 1409) andenters cube 1452, which has the first polarization selective reflector1454. The light 1472 has a first polarization and passes through thefirst polarization selective reflector 1454. The light 1472 is reflectedby the second polarization selective reflector 1456, forming reflectedlight 1474. The reflected light 1474, which maintains the firstpolarization, passes through the first polarization selective reflector1454, and leaves the cube 1452. The light 1474 passes through thequarter-wave plate 1409, and the mirror 1408 reflects the light 1474,which has passed through the quarter-wave plate 1409 once, as reflectedlight 1476. The reflected light 1476 passes through the quarter-waveplate 1409 again, and has a polarization that is orthogonal to the firstpolarization. The reflected light 1476 enters the cube 1452 once againand the first polarization selective reflector 1454 reflects the light1476 as light 1478. The first polarization selective reflector 1454directs the light 1478, having the second polarization, distinct fromthe first polarization, toward a spatial light modulator.

FIG. 14E shows an illumination system 1471. Light 1482 passes through anaperture 1410 in the mirror 1408 (and the quarter-wave plate 1409) intothe cube 1455, which has the first polarization selective reflector1458. The light 1482 has a second polarization and is reflected by boththe first polarization selective reflector 1458 and the secondpolarization selective reflector 1456, to form reflected light 1484. Thelight 1484, after reflecting off the first polarization selectivereflector 1458, leaves the cube 1455 passes through the quarter-waveplate 1409, and the mirror 1408 reflects the light 1484, which haspassed through the quarter-wave plate 1409 once, as light 1486. Thereflected light 1486 passes through the quarter-wave plate 1409 again,emerging with a polarization that is orthogonal to the secondpolarization. The reflected light 1486 enters the cube 1455 and thefirst polarization selective reflector 1458 transmits the light 1486 aslight 1488. The first polarization selective reflector 1458 directs thelight 1488 towards a spatial light modulator.

In some embodiments, illumination systems and image projection systemsare configured such that the polarization selective reflector is apolarization volume hologram (described with respect to FIGS. 16A-16D)instead of a reflective polarizer.

FIG. 15A shows a system 1500 similar to the compact illumination system1400 described in FIG. 14A. A difference between the system 1500 and theillumination system 1400 is that a first polarization volume hologram(PVH) 1514 is placed at the location of the first polarization selectivereflector 1414 in the compact illumination system 1400, replacing thefirst polarization selective reflector 1414. In some embodiments, thesecond polarization selective reflector 1416 in the compact illuminationsystem 1400 is replaced by a second PVH 1516 in the system 1500. Thelight source 1402 emits light 1520 toward the diverting optic 1406.Light 1522 from the diverting optic 1406 may be partially collimated.Light 1522 from the diverting optic 1406 enters the polarizing beamsplitter 1502 of the system 1500. In some embodiments, the light 1522 ispolarized. In some embodiments, the light 1522 has a nonplanarpolarization. Nonplanar polarization refers to any of polarizations thatare not linearly-polarized (e.g., elliptically polarized light andcircularly polarized light). In some cases, the light 1522 is circularlypolarized. FIG. 15A shows embodiments in which the light 1522 is leftcircularly polarized. However, a person having ordinary skill in the artwould understand that a system may be configured for an incoming lighthaving right circular polarization. The handedness of the circularlypolarized light traversing such system would be reversed from thosedenoted in FIG. 15A. For brevity, details of such system are notrepeated herein.

Depending on the configuration (e.g., handedness of liquid crystals inthe PVH), PVH transmits a first circularly polarized light (e.g., leftcircularly polarized light) and reflects a second circularly polarizedlight (e.g., right circularly polarized light) that is orthogonal to thefirst circularly polarized light, or vice versa. In FIG. 15A, the firstPVH 1514 directs the light 1522 (e.g., transmits the light 1522) towardthe second PVH 1516, which reflects the light 1522 as light 1524. Thelight 1524 maintains the left circular polarization. The first PVH 1514directs the light 1524 (e.g., transmits the light 1524) out of thepolarizing beam splitter 1502, toward the mirror 1408 so that the mirror1408 reflects light 1524 as reflected light 1526. In FIG. 15 , thesystem 1500 does not include the quarter-wave plate 1409, as the light1526 has a circular polarization (e.g., right circular polarization)orthogonal to the circular polarization of the light 1524 (e.g., leftcircular polarization) without having to pass through any quarter-waveplate.

The first PVH 1514 reflects the light 1526 as reflected light 1528,while keeping the right circular polarization of the reflected light1528. The reflected light 1528 leaves the polarizing beam splitter 1502and passes toward the spatial light modulator 1430. In some embodiments,the system includes a SLM window 1418 (or cover glass) between the beamsplitter 1502 and the spatial light modulator 1430.

The spatial light modulator 1430 creates spatially modulated patterns ofreflected light 1530, modifying a polarization of the reflected light1530 such that the reflected light 1530 (or a portion thereof) passesthrough the first PVH 1514 (e.g., the spatial light modulator 1430converts a polarization of the light 1530 to be orthogonal to apolarization of the light 1528). The first PVH 1514 directs the light1530 to a reflective lens assembly 1541, which refracts and reflects thelight 1530, as light 1532. The reflective lens assembly 1541 differsfrom the reflective lens assembly 1440 in that the reflective lensassembly does not include (or is not coupled with) a quarter-wave platein the assembly. The light 1532 has a polarization (e.g., right circularpolarization) orthogonal to the polarization of the light 1530 (e.g.,left circular polarization). The first PVH 1514 reflects the light 1532as light 1534, while keeping the light 1534 as right circularlypolarized. The light 1534, being right-circularly polarized, passesthrough optional optics 1442 and exits the beam splitter 1502. In someembodiments, the light 1534 enters waveguide 1444.

In some embodiments, the first PVH 1514 defines a first plane (e.g., aplane making a 45 degree angle with the x-y plane shown in FIG. 15A). Insome embodiments, the second PVH 1516 defines a second plane parallel tothe x-y plane. In some embodiments, the first plane intersects thesecond plane at a first acute angle (e.g., 45 degree). In someembodiments, the mirror 1408 defines a third plane parallel to the x-yplane. In some embodiments, the mirror 1408 has a planar surface. Insome embodiments, the mirror 1408 has a curved surface. In some cases,when the mirror 1408 is not planar (as shown in FIG. 15A), the thirdplane defined by the mirror 1408 perpendicularly intersects an opticalaxis of the mirror 1408, which corresponds to an axis of rotationalsymmetry for the non-planar mirror 1408. In some embodiments, the firstplane intersects and makes a second acute angle (e.g., 45 degree) withthe third plane. In some embodiments, the second PVH 1516 is positionedin a first orientation that is substantially parallel to the mirror 1408(e.g., the second PVH 1516 is substantially parallel to the thirdplane).

In some embodiments, the first PVH 1514 reflects light having apolarization (e.g., right circular polarization) different from apolarization of light reflected by the second PVH 1516 (e.g., leftcircular polarization).

FIG. 15B shows a compact spatial light modulator imaging system 1550having a light source 1402, an integrator rod 1404, and a divertingoptic 1406, as described in reference to FIG. 14A. The polarizing beamsplitter 1551 includes a first PVH 1554 and a second PVH 1556. Leftcircularly polarized light 1522 is reflected by the first PVH 1554toward the spatial light modulator 1430. The spatial light modulator1430 creates spatially modulated patterns of reflected light 1540,modifying a polarization of the reflected light 1538 (or a portionthereof) such that the reflected light 1540 (or a portion thereof)passes through the first PVH 1554 (e.g., turning a polarization of thelight 1540 to be orthogonal to a polarization of the light 1538). Thefirst PVH 1554 directs the light 1540 to the reflective lens assembly1541, which refracts and reflects the light 1540, as light 1542. Thelight 1542 has a polarization (e.g., right circular polarization)orthogonal to a polarization of the light 1540 (e.g., left circularpolarization). The first PVH 1554 reflects the light 1542 as light 1544,while keeping the light 1544 as right circularly polarized. The light1544 passes through optional optics 1442 and enters into the waveguide1444.

In some embodiments, the polarizing beam splitter 1551 has a dimension(e.g., along the x-direction) lengthened, to capture a larger field ofview, similar to the description of FIGS. 12B and FIG. 12C. In suchcases, a projection of the first polarization selective reflector on aplane defined by the spatial light modulator 1430 (e.g., along the z-xplane) has a rectangular shape.

Polarization Volume Hologram (PVH)

FIGS. 16A-16D are schematic diagrams illustrating a polarization volumehologram (PVH) 1600 in accordance with some embodiments. In someembodiments, the PVH 1600 is a liquid crystal PVH including a layer ofliquid crystals arranged in helical structures (e.g., a liquid crystalformed of a cholesteric liquid crystal). PVH is selective with respectto circular polarization of light. When state (handedness) of thecircularly polarized light is along a helical axis of a liquid crystal,the PVH interacts with the circularly polarized light and therebychanges the direction of the light (e.g., reflects, refracts ordiffracts the light). Concurrently, while changing the direction of thelight, the PVH also changes the polarization of the light. In contrast,the PVH transmits light with opposite circular polarization withoutchanging its direction or polarization. For example, a PVH changespolarization of right circularly polarized (RCP) light to leftcircularly polarized (LCP) light and simultaneously redirects the lightwhile transmitting LCP light without changing its polarization ordirection. In some embodiments, a PVH is also selective on wavelengthrange and/or on an incident angle. If the incident light is at thedesigned wavelength, RCP light is redirected and converted to LCP lightwhile RCP light with wavelength outside the designed wavelength range istransmitted without its polarization converted. If the incident lighthas an incident angle at the designed incident angle range, RCP light isconverted to LCP light and redirected while RCP light with an incidentangle outside the designed incident angle range is transmitted withoutits polarization converted.

FIG. 16A illustrates a three dimensional view of PVH 1600 with incominglight 1604 entering the grating along the z-axis. FIG. 16B illustratesan x-y-plane view of PVH 1600 with a plurality of liquid crystals (e.g.,liquid crystals 1602-1 and 1602-2) with various orientations. Theorientations of the liquid crystals are constant along reference linebetween A and A′ along the x-axis, as shown in FIG. 16D illustrating adetailed plane view of the liquid crystals along the reference line.FIG. 16C illustrates a y-z-cross-sectional view of PVH 1600. In FIG.16C, a pitch 1612 defined as a distance along the z-axis at which anazimuth angle of a liquid crystal has rotated 180 degrees is constantthroughout the grating. However, in some embodiments, the pitch may varyalong the z-axis. In FIG. 16C, PVH 1600 has helical structures 1608 withhelical axes aligned corresponding to the z-axis. However, in someembodiments, the helical axes may be tilted from the z-axis. The helicalstructures create a volume grating with a plurality of diffractionplanes (e.g., planes 1610-1 and 1610-2). The diffraction planes of PVH1600 extend across the grating. In FIG. 16C, diffraction planes 1610-1and 1610-2 are tilted with respect to the z-axis. Helical structures1608 define the polarization selectivity of PVH 1600, as light withcircular polarization handedness corresponding to the helical axes isdiffracted while light with circular polarization with the oppositehandedness is not diffracted. Helical structures 1608 also define thewavelength selectivity of PVH 1600, as light with wavelength close to ahelical pitch (e.g., helical pitch 1612 in FIG. 16C) is diffracted whilelight with other wavelengths is not diffracted.

In some embodiments, the PVH 1514, the PVH 1516, the PVH 1554, and thePVH 1556 described with respect to FIGS. 15A and 15B are cholestericliquid crystal (CLC) gratings. A CLC grating has similar opticalproperties to those described with respect to PVH 1600. A CLC and a PVHboth include liquid crystals in helical arrangements. In someembodiments, the liquid crystals are cholesteric liquid crystals. CLCgrating further includes a photoalignment layer and the CLCs arearranged to helical structures in accordance with the photoalignmentlayer. In contrast, in a PVH, CLCs are arranged to helical structures inaccordance with holographic recording (e.g., without a photoalignmentlayer).

In some embodiments, at least one of: a first polarization selectivereflector (e.g., first PVH 1514) and a second polarization selectivereflector (e.g., second PVH 1516) is a metasurface. In some embodiments,at least one of: a first polarization selective reflector (e.g., firstPVH 1514) or a second polarization selective reflector (e.g., second PVH1516) includes resonant structures, a chiral layer, and/or abirefringent material. In some embodiments, at least one of: a firstpolarization selective reflector (e.g., first PVH 1514) and a secondpolarization selective reflector (e.g., second PVH 1516) is a liquidcrystal based polarization selective element. In some embodiments, theliquid crystal based polarization selective element includes cholestericliquid crystals.

In some embodiments, a first polarization selective reflector (e.g.,reflective polarizer or PVH) defines a first plane (e.g., a plane makinga 45 degree angle with the x-y plane shown in FIG. 15A). In someembodiments, a second polarization selective reflector (e.g., reflectivepolarizer or PVH) defines a second plane parallel to the x-y plane. Insome embodiments, the first plane intersects the second plane at a firstacute angle (e.g., 45 degree). In some embodiments, a reflector (e.g.,mirror 1408) defines a third plane parallel to the x-y plane. In somecases, when the reflector is not planar, the third plane is defined as aplane that perpendicularly intersects an optical axis of the non-planarmirror. In some cases, the optical axis of the non-planar mirror is itsaxis of rotational symmetry (e.g., along the z-axis). The third planethat perpendicularly intersects the z-axis is a plane parallel to thex-y plane. In some embodiments, the first plane intersects and makes asecond acute angle (e.g., 45 degree) with the third plane. In someembodiments, the second polarization selective reflector is positionedin a first orientation that is substantially parallel to the reflector.

In some embodiments, the first angle is measured from a portion of thefirst plane that directs a first light (e.g., light 1522) to a portionof the second plane that directs a second light (e.g., light 1524).

In some embodiments, the polarizing beam splitter includes a prismassembly, and the first polarization selective reflector is disposedalong a diagonal of the prism assembly. In some embodiments, thediagonal is an inner diagonal (e.g., the first polarization selectivereflector is sandwiched between two prisms of the prism assembly, likethe polarization selective reflector 1454 in the cube 1452 shown in FIG.14B and the polarization selective reflector 1458 in the cube 1455 shownin FIG. 14C).

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationdifferent from a polarization of light reflected by the secondpolarization selective reflector (e.g., similar to the pair ofpolarization selective reflector 1454 and the polarization selectivereflector 1456 in FIG. 14B).

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationidentical to a polarization of light reflected by the secondpolarization selective reflector (e.g., similar to the pair ofpolarization selective reflector 1458 and the polarization selectivereflector 1456 in FIG. 14C).

In light of these principles, we turn to certain embodiments.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned in a first orientation sothat the first polarization selective reflector receives first light ina first direction, redirects a first portion, of the first light, havinga first polarization to a second direction that is non-parallel to thefirst direction; and receives second light in a third direction andtransmit a first portion, of the second light, having a secondpolarization orthogonal to the first polarization. The optical deviceincludes a second polarization selective reflector positioned in asecond orientation non-parallel to the first orientation, and adjacentto the first polarization selective reflector so that the secondpolarization selective reflector receives third light in a fourthdirection; redirects a first portion, of the third light, having thefirst polarization to a fifth direction that is non-parallel to thefourth direction; and receives fourth light in a sixth direction andtransmit a first portion, of the fourth light having the secondpolarization (e.g., FIGS. 4A-10B).

In some embodiments, the second direction is orthogonal to the firstdirection and the fifth direction is orthogonal to the third direction(e.g., FIGS. 4A-10B).

In some embodiments, the first polarization selective reflector isfurther configured to transmit a second portion, of the first light,having the second polarization; and the second polarization selectivereflector is further configured to receive, and transmit, the secondportion, of the first light having the second polarization (e.g., FIGS.4A-10B).

In some embodiments, the optical device further includes a thirdreflector configured to receive from the second polarization selectivereflector the second portion of the first light, and redirect the secondportion of the first light back to the second polarization selectivereflector as the second light (e.g., FIGS. 4A-10B).

In some embodiments, the optical device further includes a light sourceconfigured to output the first light having the first polarization.

In some embodiments, the optical device further includes an opticalintegrator configured receive the first light and redirect the firstlight such that the first light transmitted by the optical integratorhas a smaller divergence than the first light incident on the opticalintegrator. In some embodiments, the optical device further includes aFresnel reflector optically coupled with the first polarizationselective reflector, the Fresnel reflector configured to receive thefirst light output by the light source; and redirect the first lighttoward the first polarization selective reflector. In some embodiments,the Fresnel reflector is configured to expand a beam size of the firstlight (e.g., FIGS. 8A-9 ).

In some embodiments, the optical device further includes a waveplatedisposed between the third reflector and the second polarizationselective reflector. In some embodiments, the waveplate is configured toconvert linearly polarized light to circularly polarized light and toconvert circularly polarized light to linearly polarized light (e.g., aquarter-wave plate). In some embodiments, the first polarizationselective reflector is further configured to reflect a second portion,of the second light, having the first polarization in a seventhdirection distinct from the third direction; and the second polarizationselective reflector is further configured to reflect a second portion,of the fourth light, having the first polarization, in an eighthdirection distinct from the sixth direction.

In some embodiments, the optical device further includes a reflectivespatial light modulator optically coupled with the first polarizationselective reflector and the second polarization selective reflector, thereflective spatial light modulator configured to: receive, on a firstregion of the reflective spatial light modulator, the first portion ofthe first light having the first polarization and reflect the firstportion of the first light as the second light. The reflective spatiallight modulator is also configured to receive, on a second regionadjacent to the first region of the reflective spatial light modulator,the first portion of the third light having the first polarization andreflect the first portion of the third light as the fourth light.

In some embodiments, the reflective spatial light modulator includes areflective surface and a plurality of pixels, a respective pixel in theplurality of pixels having respective modulating elements. In someembodiments, reflecting the first portion of the first light as thesecond light and reflecting the first portion of the third light as thefourth light includes modulating, by the respective modulating elements,polarization of the first portion of the first light and the firstportion of the third light.

In some embodiments, the reflective spatial light modulator is a LiquidCrystal on Silicon (LCoS) display. In some embodiments, the firstpolarization selective reflector in the first orientation and the secondpolarization selective reflector in the second orientation define anangle that is approximately 90 degrees. (e.g., FIGS. 4A, 4B, and 7B). Insome embodiments, the angle is more or less than 90 degrees (e.g., FIG.4C). The first polarization selective reflector and the secondpolarization selective reflector are coupled to each other (e.g., FIGS.4A, 4B, 7B and 7C).

In some embodiments, the optical device further includes a prismdefining a first facet and a second facet. The first polarizationselective reflector is disposed on the first facet and the secondpolarization selective reflector is disposed on the second facet (FIGS.7B and 7C). In some embodiments, the first polarization selectivereflector and the second polarization selective reflector are selectedfrom the group consisting of: a wire grid polarizer, a birefringentoptical film reflective polarizer, a cholesteric reflective polarizer,and a MacNeille polarizer.

In some embodiments, the optical device further includes a first lightsource configured to output the first light having the firstpolarization; and a second light source configured to output the thirdlight having the first polarization (e.g., FIG. 9 ).

In some embodiments, the optical device further includes a first Fresnelreflector optically coupled with the first polarization selectivereflector configured to receive the first light output by the firstlight source; and redirect the first light toward the first polarizationselective reflector in the first direction. The optical device furtherincludes a second Fresnel reflector optically coupled with the secondpolarization selective reflector configured to receive the third lightoutput by the second light source; and redirect the third light towardthe second polarization selective reflector in the fourth direction.

In some embodiments, the fourth direction is substantially parallel tothe first direction. In some embodiments, the fifth direction issubstantially parallel to the second direction. In some embodiments, thefifth direction is non-parallel to the second direction.

In accordance with some embodiments, a method includes, with a firstpolarization selective reflector positioned in a first orientation,receiving first light in a first direction; redirecting a first portion,of the first light, having a first polarization to a second directionthat is non-parallel to the first direction. The method includesreceiving second light in a third direction, transmit a first portion,of the second light having a second polarization orthogonal to the firstpolarization. The method also includes, with a second polarizationselective reflector positioned in a second orientation non-parallel tothe first orientation, and adjacent to the first polarization selectivereflector, receiving third light in a fourth direction; redirecting afirst portion, of the third light, having the first polarization to afifth direction that is non-parallel to the fourth direction; andreceiving fourth light in a sixth direction, transmit a first portion,of the fourth light having the second polarization (e.g., FIGS. 4A-10B).

In accordance with some embodiments, a method of making an opticalassembly includes placing a first polarization selective reflector in afirst orientation; and placing a second polarization selective reflectorin a second orientation non-parallel, and adjacent, to the firstorientation. In some embodiments, the optical assembly includes apolarization beam splitter (e.g., FIGS. 4A-10B).

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector, a second polarization selectivereflector; and a third reflector. The first polarization selectivereflector is configured to receive first light and redirect a firstportion, of the first light, having a first polarization and transmit asecond portion, of the first light, having a second polarizationorthogonal to the first polarization. The second polarization selectivereflector is configured to receive from the first polarization selectivereflector, and transmit to the third reflector, the second portion ofthe first light. The third reflector is configured to receive from thesecond polarization selective reflector, and redirect back to the secondpolarization selective reflector, the second portion of the first light;and the second polarization selective reflector is further configured toreceive light from the third reflector and redirect at least a portionof light, the redirected portion having the first polarization (e.g.,FIGS. 4A-10B).

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned relative to a spatial lightmodulator; and a first reflective assembly positioned relative to thefirst polarization selective reflector so that the first polarizationselective reflector receives first light from the spatial lightmodulator and directs at least a portion of the first light having afirst polarization toward the first reflective assembly as second light.The first reflective assembly receives the second light from the firstpolarization selective reflector and directs at least a portion of thesecond light toward the first polarization selective reflector as thirdlight having a second polarization. The second polarization is distinctfrom the first polarization (e.g., FIGS. 11A and 11B).

In some embodiments, the spatial light modulator is positioned in afirst direction from the first polarization selective reflector, and thefirst reflective assembly is positioned in a second direction from thefirst polarization selective reflector. In some embodiments,illumination light enters the optical device in a third direction fromthe first polarization selective reflector; and a waveguide ispositioned in a fourth direction from the first polarization selectivereflector. The first direction and the second direction are distinctfrom each other (e.g., FIGS. 11A and 11B).

In some embodiments, the first direction is perpendicular to the thirddirection; and the second direction is perpendicular to the fourthdirection. In some embodiments, the spatial light modulator and thefirst reflective assembly are located in opposite directions from thefirst polarization selective reflector. In some embodiments, the seconddirection is perpendicular to the third direction; and the firstdirection is perpendicular to the fourth direction. In some embodiments,the waveguide and the first reflective assembly are located in oppositedirections from the first polarization selective reflector.

In some embodiments, the optical device further includes a firstreflector. The first reflector defines an opening, and the firstreflector is positioned relative to the spatial light modulator so thatthe spatial light modulator receives light that has (i) passed throughthe opening of the first reflector and (ii) subsequently reflected offthe first reflector. In some embodiments, a second polarizationselective reflector is disposed adjacent to the waveguide. The secondpolarization selective reflector is configured (e.g., by orienting apolarization axis of the second polarization selective reflector) toreflect light having a polarization different (e.g., orthogonal) from apolarization of light reflected by the first polarization selectivereflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to the waveguide. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization identical to apolarization of light reflected by the first polarization selectivereflector. In some embodiments, a first plane defined by (e.g.,containing) the first polarization selective reflector intersects asecond plane defined by (e.g., containing) the spatial light modulatorat a first acute angle. The first reflective assembly includes apolarization retarder and a reflective lens.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by the spatial light modulator has arectangular shape. In some embodiments, a height of the projection isgreater than a width of the projection so that a field of view of thespatial light modulator along the height dimension is larger than afield of view along the width dimension.

In some embodiments, the first polarization selective reflector is atsubstantially 45-degree angle relative to the plane defined by thespatial light modulator. In some embodiments, the optical deviceincludes a first prism and a second prism. In some embodiments, at leasta portion of the first prism has a trapezoidal cross-section having afirst edge, a second edge, a third edge, a fourth edge. The first edgeis perpendicular to the second edge; the second prism is a right-angleprism having a hypotenuse; and the first polarization selectivereflector is disposed between the first prism and the second prism,parallel to the hypotenuse of the second prism and the fourth edge ofthe first prism. In some embodiments, a length of the hypotenuse isequal to a length of the third edge. In some embodiments, the firstreflective assembly is positioned relative to the spatial lightmodulator so that the first polarization selective reflector directs thesecond light toward the first reflective assembly by transmitting thesecond light.

In some embodiments, the first reflective assembly is positionedrelative to the spatial light modulator so that the first polarizationselective reflector directs the second light having the firstpolarization toward the first reflective assembly by reflecting thesecond light. In some embodiments, the first reflective assemblyincludes a reflector and a polarization retarder disposed adjacent tothe reflector.

In some embodiments, the polarization retarder includes a quarter-waveplate. In some embodiments, the polarization retarder is disposed on afirst surface of a lens and the reflector includes a reflective coatingdisposed on an opposing second surface of the lens.

In accordance to some embodiments, a method includes directing, using afirst polarization selective reflector, first light from a spatial lightmodulator toward a first reflector assembly. The method includesreceiving, using the first reflector assembly, the first light anddirecting at least a portion of the first light toward the firstpolarization selective reflector as second light. The method alsoincludes receiving, using the first polarization selective reflector,the second light and directing at least a portion of the second lighttoward a waveguide (e.g., as third light). The first light has a firstpolarization, and the second light has a second polarization distinctfrom the first polarization (e.g., the second polarization is orthogonalto the first polarization).

In some embodiments, the first polarization selective reflectortransmits the first light toward the first reflector assembly. In someembodiments, the first polarization selective reflector reflects thefirst light toward the first reflector assembly.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector, a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light (e.g., impinging on the first polarization selectivereflector and having a first polarization) toward the secondpolarization selective reflector and the second polarization selectivereflector directs at least a portion of the first light toward the firstpolarization selective reflector as second light. The optical deviceincludes a first reflector positioned relative to the first polarizationselective reflector so that the first polarization selective reflectordirects at least a portion of the second light received from the secondpolarization selective reflector toward the first reflector as thirdlight and the first reflector directs at least a portion of third light(e.g., back) toward the first polarization selective reflector (e.g.,FIG. 14A).

In some embodiments, the first reflector is aspherical. In someembodiments, the first reflector is aspherical to provide uniformillumination at the spatial light modulator.

In some embodiments, the first polarization selective reflector isconfigured to direct the portion of the third light from the firstreflector toward a spatial light modulator. In some embodiments, theoptical device further includes a second reflector positioned relativeto the first polarization selective reflector so that light from thespatial light modulator is directed by the first polarization selectivereflector toward the second reflector and the second reflector directsat least a portion of the light from the spatial light modulator towardsthe first polarization selective reflector. In some embodiments, thesecond reflector projects at least a portion of the light from thespatial light modulator.

In some embodiments, the second polarization selective reflector ispositioned in a first orientation substantially parallel to a plane thatperpendicularly intersects an optical axis of the first reflector. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization different from (e.g.,orthogonal to) a polarization of light reflected by the firstpolarization selective reflector.

In some embodiments, the first polarization selective reflector directsthe first light (having the first polarization) toward the secondpolarization selective reflector by transmitting the first light. Insome embodiments, the second light directed toward the firstpolarization selective reflector by the second polarization selectivereflector is transmitted through the first polarization selectivereflector.

In some embodiments, the first polarization selective reflector directsthe portion of the third light from the first reflector toward a spatiallight modulator by reflecting the portion of the third light. In someembodiments, the first polarization selective reflector has a firstsurface and an opposing second surface, the first reflector faces thefirst surface, and the second polarization selective reflector faces thesecond surface.

In some embodiments, the second polarization selective reflector ispositioned in a second orientation substantially orthogonal to a planethat perpendicularly intersects an optical axis of the first reflector.In some embodiments, the second polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the secondpolarization selective reflector) to reflect light having an identicalpolarization as light reflected by the first polarization selectivereflector. In some embodiments, (e.g., FIG. 14E) the first polarizationselective reflector has a first surface and an opposite second surface,both the first reflector and the second polarization selective reflectorface the first surface.

In some embodiments, the first polarization selective reflector directsthe first light (having the first polarization) toward the secondpolarization selective reflector by reflecting the first light towardthe second polarization selective reflector.

In some embodiments, the portion of the second light directed toward thefirst polarization selective reflector by the second polarizationselective reflector is reflected by the first polarization selectivereflector toward the first reflector.

In some embodiments, the first polarization selective reflector directsthe portion of the third light from the first reflector toward thespatial light modulator by transmitting the portion of the third light.In some embodiments, the first polarization selective reflector has afirst surface and an opposing second surface, and the first surface ofthe first polarization selective reflector faces both the firstreflector and the second polarization selective reflector.

In some embodiments, the first reflector includes structures configuredto scatter the portion of the third light directed toward the firstpolarization selective reflector.

In some embodiments, a first plane defined by (e.g., containing) thefirst polarization selective reflector intersects, at a first acuteangle, with a second plane defined by (e.g., containing) the secondpolarization selective reflector, and intersects, at a second acuteangle, with a third plane defined by (e.g., containing) the firstreflector.

In some embodiments, the optical device further includes a firstpolarization retarder disposed adjacent to the first reflector. In someembodiments, the first reflector defines a first opening so that thefirst light received by the first polarization selective reflector haspassed through the first opening.

In some embodiments, an illumination system includes the optical device,a light source, a homogenizing device configured to condition light fromthe light source as output light. The illumination system includes adiverting optic positioned to direct the output light into the opticaldevice through the first opening.

In some embodiments, the first polarization retarder defines a secondopening aligned with the first opening of the first reflector.

In accordance to some embodiments, a method includes directing, using afirst polarization selective reflector, first light toward a secondpolarization selective reflector. The method includes receiving, usingthe second polarization selective reflector, the first light anddirecting at least a portion of the first light toward the firstpolarization selective reflector as second light. The method includesreceiving, using the first polarization selective reflector, the secondlight and directing at least a portion of the second light toward afirst reflector as third light. The method also includes receiving,using the first reflector, the third light and directing at least aportion of the third light toward the first polarization selectivereflector as fourth light. The method includes receiving, using thefirst polarization selective reflector, the fourth light and directingat least a portion of the fourth light to illuminate a spatial lightmodulator.

In some embodiments, an optical device includes a first polarizationselective reflector, a second polarization selective reflectorpositioned relative to the first polarization selective reflector sothat the first polarization selective reflector directs light impingingon the first polarization selective reflector and having a firstpolarization toward the second polarization selective reflector and thesecond polarization selective reflector directs at least a portion ofthe light (back) toward the first polarization selective reflector. Theoptical device includes a first reflector positioned relative to thefirst polarization selective reflector so that the first polarizationselective reflector directs the light received from the secondpolarization selective reflector toward the first reflector as secondlight and the first reflector directs at least a portion of the secondlight (back) toward the first polarization selective reflector.

In some embodiments, the first polarization selective reflector isconfigured to direct the light from the first reflector toward a spatiallight modulator.

In some embodiments, the first polarization selective reflector receivesfirst light from a first direction and directs a portion of the firstlight having a first polarization in a second direction (e.g., theportion of the first light is light 1422 in FIG. 14A, light 1464 in FIG.14C, and light 1482 in FIG. 14E). In some embodiments, the firstdirection is collinear with the second direction (e.g., light 1472 inFIG. 14D).

In some embodiments, the first polarization selective reflector receivessecond light from a third direction and directs a portion of the secondlight having a second polarization in a fourth direction (e.g., in someembodiments, the second light is light 1434 in FIG. 14A; light 1484 inFIG. 14E; light 1465 in FIG. 14C is an example of “a portion of thesecond light in a fourth direction”). In some embodiments, the thirddirection is collinear with the fourth direction (e.g., light 1474 inFIG. 14D is second light in which the third direction is collinear withthe fourth direction).

In some embodiments, the optical device includes a second polarizationselective reflector positioned in a first orientation non-parallel tothe first polarization selective reflector for receiving third lightfrom a fifth direction and directing a portion of the third light havinga third polarization in a sixth direction.

In some embodiments, the optical device includes a first reflectorpositioned in a second orientation non-parallel to the firstpolarization selective reflector for receiving fourth light from aseventh direction and directing a portion of the fourth light in aneighth direction, the fourth light (e.g., received by the firstreflector) having a fourth polarization and the portion of the fourthlight (e.g., directed by the first reflector) having a fifthpolarization.

In some embodiments, an optical device includes a first polarizationselective reflector for receiving first light from a first direction anddirecting a portion of the first light having a first polarization in asecond direction. The first polarization selective reflector receivessecond light from a third direction and directs a portion of the secondlight having a second polarization in a fourth direction.

In some embodiments, the optical device includes a second polarizationselective reflector positioned in a first orientation non-parallel tothe first polarization selective reflector for receiving third lightfrom a fifth direction and directing a portion of the third light havinga third polarization in a sixth direction.

In some embodiments, the optical device includes a first reflectorpositioned in a second orientation non-parallel to the firstpolarization selective reflector for receiving fourth light from aseventh direction and directing a portion of the fourth light in aneighth direction. The fourth light (e.g., received by the firstreflector) has a fourth polarization and the portion of the fourth light(e.g., directed by the first reflector) has a fifth polarization.

In some embodiments, the first reflector defines a first opening so thatthe first polarization selective reflector receives light that haspassed through the first opening. In some embodiments, the opticaldevice further includes a first polarization retarder disposed adjacentto the first reflector. In some embodiments, the first polarizationretarder defines a second opening aligned with the first opening of thefirst reflector.

In some embodiments, the first polarization retarder is configured to:(i) direct the fourth light having the fourth polarization (e.g., LCP)to the first reflector in the seventh direction; (ii) receive, from thefirst reflector, the portion of the fourth light having the fifthpolarization (e.g., RCP), propagating in the eighth direction; and (iii)convert the portion of the fourth light having the fifth polarization,into fifth light having a sixth polarization (e.g., verticallypolarized).

In accordance to some embodiments, an illumination system includes theoptical device, a spatial light modulator positioned relative to theoptical device for receiving the portion of the first light having thefirst polarization in the second direction from the first polarizationselective reflector. The illumination system includes a second reflectorpositioned relative to the optical device for directing, along the thirddirection, the second light towards the first polarization selectivereflector. The fourth direction is non-parallel to the third direction,and the first polarization is parallel to the second polarization (e.g.,FIG. 14A).

In some embodiments, the second reflector includes a reflective lensstack, and the reflective lens stack includes a second polarizationretarder.

In some embodiments, an illumination system includes the optical device,and a spatial light modulator. The second light from the third directionis the fifth light having the sixth polarization. In some embodiments,the spatial light modulator receives the portion of the second lighthaving the second polarization in the fourth direction from the firstpolarization selective reflector. The first direction is collinear withthe second direction and the fifth direction. The portion of the thirdlight in the sixth direction is transmitted through the firstpolarization selective reflector and is directed by the firstpolarization retarder, as the fourth light having the fourthpolarization, to the first reflector (e.g., FIG. 14D).

In some embodiments, an illumination system includes the optical deviceand a spatial light modulator. The spatial light modulator receives thefifth light having the sixth polarization from the first polarizationretarder. In some embodiments, the second direction is collinear withthe fifth direction. The third direction is collinear with the sixthdirection. The fourth direction is collinear with the seventh direction,and the first polarization is parallel to the second polarization (FIG.14E).

In some embodiments, the first polarization selective reflector isdisposed on a diagonal of the optical device and a first planecontaining the first polarization selective reflector: (i) intersects,at a first acute angle, with a second plane containing the firstpolarization selective reflector, and (ii) intersects, at a second acuteangle, with a third plane containing the first reflector.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector; a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light having a first nonplanar polarization (e.g., a circularpolarization or an elliptical polarization) toward the secondpolarization selective reflector and the second polarization selectivereflector directs at least a portion of the first light toward the firstpolarization selective reflector as second light. The optical devicealso includes a first reflector positioned relative to the firstpolarization selective reflector so that the first polarizationselective reflector directs at least a portion of the second light(received from the second polarization selective reflector) having asecond nonplanar polarization toward the first reflector as third light.In some embodiments, the first reflector directs at least a portion ofthird light toward the first polarization selective reflector (e.g.,FIGS. 15A and 15B).

In some embodiments, the first polarization selective reflector or thesecond polarization selective reflector is a polarization element thatincludes a metasurface, resonant structures, a chiral layer, or abirefringent material.

In some embodiments, the first reflector directs at least a portion ofthird light having the first nonplanar polarization toward the firstpolarization selective reflector, and the first polarization selectivereflector is configured to direct the portion of the third light fromthe first reflector toward a spatial light modulator as illuminationlight.

In some embodiments, the first polarization selective reflector is aliquid crystal based polarization selective element. In someembodiments, the liquid crystal based polarization selective elementincludes a polarization volume hologram. In some embodiments, the liquidcrystal based polarization selective element includes cholesteric liquidcrystals.

In some embodiments, the optical device further includes a firstreflective assembly positioned relative to the first polarizationselective reflector so that the first polarization selective reflectorreceives first imaging light from a spatial light modulator and directsat least a portion of the first imaging light having a third nonplanarpolarization toward the first reflective assembly as second imaginglight. The first reflective assembly receives the second imaging lightfrom the first polarization selective reflector and directs at least aportion of the second imaging light toward the first polarizationselective reflector as third imaging light having a fourth nonplanarpolarization. The third nonplanar polarization is distinct from thefourth nonplanar polarization.

In some embodiments, the second polarization selective reflector ispositioned in a first orientation that is substantially parallel to aplane that perpendicularly intersects an optical axis of the firstreflector, and the second polarization selective reflector is configured(e.g., by orienting a polarization axis of the second polarizationselective reflector) to reflect light having a polarization differentfrom a polarization of light reflected by the first polarizationselective reflector.

In some embodiments, a first plane defined by the first polarizationselective reflector intersects, at a first acute angle, with a secondplane defined by the second polarization selective reflector, andintersects, at a second acute angle, with a third plane defined by thefirst reflector.

In some embodiments, the first reflector defines a first opening so thatthe first light received by the first polarization selective reflectorhas passed through the first opening.

In some embodiments, an illumination system includes the optical device,a light source; a homogenizing device configured to condition light fromthe light source as output light; and a diverting optic positioned todirect the output light into the optical device through the firstopening.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector positioned relative to a spatial lightmodulator; and a first reflective assembly positioned relative to thefirst polarization selective reflector so that the first polarizationselective reflector receives first light from the spatial lightmodulator and directs at least a portion of the first light having afirst nonplanar polarization toward the first reflective assembly assecond light. The first reflective assembly receives the second lightfrom the first polarization selective reflector and directs at least aportion of the second light having a second nonplanar polarizationtoward the first polarization selective reflector as third light. Thesecond nonplanar polarization is distinct from the first nonplanarpolarization.

In some embodiments, the first polarization selective reflector is apolarization element that includes a metasurface, resonant structures, achiral layer, or a birefringent material.

In some embodiments, the first polarization selective reflector is aliquid crystal based polarization selective element. In someembodiments, the optical device further includes a first reflector. Insome embodiments, the first reflector defines an opening. The firstreflector is positioned relative to the spatial light modulator so thatthe spatial light modulator receives light that has (i) passed throughthe opening of the first reflector and (ii) subsequently reflected offthe first reflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to a waveguide. Thesecond polarization selective reflector is configured to reflect lighthaving a polarization different from a polarization of light reflectedby the first polarization selective reflector.

In some embodiments, the optical device further includes a secondpolarization selective reflector disposed adjacent to a waveguide. Thesecond polarization selective reflector is configured (e.g., byorienting a polarization axis of the second polarization selectivereflector) to reflect light having a polarization identical to apolarization of light reflected by the first polarization selectivereflector.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by the spatial light modulator has arectangular shape.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector positioned in a first orientation sothat the first polarization selective reflector receives first light ina first direction; redirects a first portion, of the first light, havinga first nonplanar polarization to a second direction that isnon-parallel to the first direction. The first polarization selectivereflector receives second light in a third direction and transmit afirst portion, of the second light, having a second nonplanarpolarization orthogonal to the first nonplanar polarization. The opticaldevice includes a second polarization selective reflector positioned ina second orientation non-parallel to the first orientation so that thesecond polarization selective reflector receives third light in a fourthdirection; redirects a first portion, of the third light, having thefirst nonplanar polarization to a fifth direction that is non-parallelto the fourth direction; and receives fourth light in a sixth directionand transmit a first portion, of the fourth light having the secondnonplanar polarization. In some embodiments, the first orientation isadjacent to the first polarization selective reflector.

In some embodiments, the optical device further includes a thirdreflector configured to receive from the second polarization selectivereflector a second portion of the first light transmitted by the firstpolarization selective reflector, and redirect the second portion of thefirst light back to the second polarization selective reflector as thesecond light.

In some embodiments, the optical device further includes a Fresnelreflector optically coupled with the first polarization selectivereflector, the Fresnel reflector configured to receive the first lightoutput by a first light source; and redirect the first light toward thefirst polarization selective reflector.

In accordance to some embodiments, an optical device includes a firstpolarization selective reflector; and a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directsfirst light having a first polarization toward the second polarizationselective reflector and the second polarization selective reflectordirects second light having a second polarization toward the firstpolarization selective reflector. A first plane defined by the firstpolarization selective reflector intersects a second plane defined bythe second polarization selective reflector at a first angle (FIGS.4A-10B).

In some embodiments, the second light is a portion of the first light.

In some embodiments, the first angle is an acute angle, and the firstangle is measured from a portion of the first plane that directs thefirst light to a portion of the second plane that directs the secondlight. In some embodiments, the first angle is approximately 45°.

In some embodiments, the optical device further comprises a prismassembly. The first polarization selective reflector is disposed along adiagonal of the prism assembly. In some embodiments, the diagonal is aninner diagonal of the prism assembly.

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationdifferent from a polarization of light reflected by the secondpolarization selective reflector.

In some embodiments, the optical device further includes a first prism,the second polarization selective reflector is disposed on a firstsurface of the first prism, and light enters the optical device at asecond surface parallel to the first surface.

In some embodiments, the first polarization selective reflector isconfigured (e.g., by orienting a polarization axis of the firstpolarization selective reflector) to reflect light having a polarizationidentical to a polarization of light reflected by the secondpolarization selective reflector.

In some embodiments, the optical device further includes a first prism.The second polarization selective reflector is disposed on a firstsurface of the first prism, and light enters the first prism at a secondsurface perpendicular to the first surface.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by a spatial light modulator isrectangular. In some embodiments, the first polarization selectivereflector is positioned relative to a spatial light modulator to directthird light having a third polarization, distinct from the firstpolarization, along a first direction to the spatial light modulator andthe second polarization selective reflector is positioned relative tothe first polarization selective reflector to direct fourth light havingthe third polarization along the first direction to the spatial lightmodulator.

In some embodiments, a projection of the first polarization selectivereflector on a plane defined by a spatial light modulator has a firstwidth. In some embodiments, a height of the first polarization selectivereflector is larger than the first width, and the height is orthogonalto the first width.

In some embodiments, the first angle is approximately 90 degrees. Insome embodiments, the angle is more or less than 90 degrees.

In some embodiments, the optical device further includes a first prism.The first polarization selective reflector is disposed on a firstsurface of the first prism and the second polarization selectivereflector is disposed on a second surface of the first prism.

In some embodiments, the optical device further includes a second prism;and a third prism. The second prism is in contact with the secondpolarization selective reflector, and the third prism is in contact withthe first polarization selective reflector.

In some embodiments, the first polarization selective reflector isconfigured to direct first light having a first nonplanar polarization(e.g., a circular polarization or an elliptical polarization) toward thesecond polarization selective reflector and the second polarizationselective reflector is configured to direct second light having a secondnonplanar polarization toward the first polarization selectivereflector.

In some embodiments, the first polarization selective reflector isconfigured to direct first light having a first nonplanar polarization(e.g., a circular polarization or an elliptical polarization) toward thesecond polarization selective reflector and the second polarizationselective reflector is configured to direct second light having a secondnonplanar polarization toward the first polarization selectivereflector.

In some embodiments, at least one of the first polarization selectivereflector or the second polarization selective reflector is either (i) aliquid crystal based polarization selective element, or (ii) apolarization selective element that includes a metasurface, resonantstructures, a chiral layer, or a birefringent material.

In some embodiments, the first angle is an acute angle, the first angleis measured from a portion of the first plane that directs the firstlight to a portion of the second plane that directs the second light,and the first polarization selective reflector is disposed along adiagonal of the optical device.

In accordance to some embodiments, a method includes coupling a firstpolarization selective reflector to a second polarization selectivereflector so that a first plane defined by the first polarizationselective reflector intersects, at a first angle, a second plane definedby the second polarization selective reflector so that the firstpolarization selective reflector is configured to direct first lighthaving a first polarization toward the second polarization selectivereflector and the second polarization selective reflector is configuredto direct second light having a second polarization toward the firstpolarization selective reflector.

In some embodiments, coupling the first polarization selective reflectorto the second polarization selective reflector includes disposing thesecond polarization selective reflector on a first surface of a prismand disposing the second polarization selective reflector on a secondsurface of the prism. In some embodiments, the first angle isapproximately 90 degrees; and the first polarization is identical to thesecond polarization. In some embodiments, the angle is more or less than90 degrees.

In some embodiments, coupling the first polarization selective reflectorto the second polarization selective reflector includes disposing thefirst polarization selective reflector on a first surface of a firstprism and disposing the second polarization selective reflector on asecond surface of the first prism. The first angle is an acute angle;and the method also includes attaching a second prism to the firstsurface of the first prism so that the first polarization selectivereflector is disposed along a diagonal of a prism assembly that includesthe first prism and the second prism.

In some embodiments, the first polarization selective reflector includesan element selected from the group consisting of a wire grid polarizer,a MacNeille polarizer, a liquid crystal based polarization selectiveelement, and a polarization element that includes a metasurface,resonant structures, or a chiral layer.

In accordance with some embodiments, a method includes coupling a firstpolarization selective reflector to a second polarization selectivereflector by disposing the first polarization selective reflector on afirst surface of a first prism and disposing the second polarizationselective reflector on a second surface of the first prism. The methodalso includes attaching a second prism to the first surface of the firstprism so that the first polarization selective reflector is disposedalong a diagonal of a prism assembly that includes the first prism andthe second prism.

In some embodiments, coupling the first polarization selective reflectorto the second polarization selective reflector includes disposing thesecond polarization selective reflector on a first surface of a prismand disposing the second polarization selective reflector on a secondsurface of the prism.

In some embodiments, the first polarization selective reflector includesa wire grid polarizer. In some embodiments, the first polarizationselective reflector includes a MacNeille polarizer. In some embodiments,the first polarization selective reflector includes a liquid crystalbased polarization selective element. In some embodiments, apolarization element includes metasurface, resonant structures, or achiral layer.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector, a second polarization selectivereflector positioned relative to the first polarization selectivereflector so that the first polarization selective reflector directslight impinging on the first polarization selective reflector and havinga first polarization toward the second polarization selective reflectorand the second polarization selective reflector directs at least aportion of the light (back) toward the first polarization selectivereflector. The optical device includes a first reflector positionedrelative to the first polarization selective reflector so that the firstpolarization selective reflector directs the light received from thesecond polarization selective reflector toward the first reflector assecond light and the first reflector directs at least a portion of thesecond light (back) toward the first polarization selective reflector.

In some embodiments, the first polarization selective reflector isconfigured to direct the light from the first reflector toward a spatiallight modulator.

In accordance with some embodiments, an optical device includes a firstpolarization selective reflector for receiving first light from a firstdirection and directing a portion of the first light having a firstpolarization in a second direction. The first polarization selectivereflector receives second light from a third direction and directs aportion of the second light having a second polarization in a fourthdirection.

In some embodiments, the optical device includes a second polarizationselective reflector positioned in a first orientation non-parallel tothe first polarization selective reflector for receiving third lightfrom a fifth direction and directing a portion of the third light havinga third polarization in a sixth direction.

In some embodiments, the optical device includes a first reflectorpositioned in a second orientation non-parallel to the firstpolarization selective reflector for receiving fourth light from aseventh direction and directing a portion of the fourth light in aneighth direction. The fourth light (e.g., received by the firstreflector) has a fourth polarization and the portion of the fourth light(e.g., directed by the first reflector) has a fifth polarization.

In some embodiments, the first reflector defines a first opening so thatthe first polarization selective reflector receives light that haspassed through the first opening.

In some embodiments, the optical device further includes a firstpolarization retarder disposed adjacent to the first reflector. In someembodiments, the first polarization retarder defines a second openingaligned with the first opening of the first reflector.

In some embodiments, the first polarization retarder is configured to:(i) direct the fourth light having the fourth polarization (e.g., LCP)to the first reflector in the seventh direction; (ii) receive, from thefirst reflector, the portion of the fourth light having the fifthpolarization (e.g., RCP), propagating in the eighth direction; and (iii)convert the portion of the fourth light having the fifth polarization,into fifth light having a sixth polarization (e.g., verticallypolarized).

In accordance with some embodiments, an illumination system includes theoptical device, a spatial light modulator positioned relative to theoptical device for receiving the portion of the first light having thefirst polarization in the second direction from the first polarizationselective reflector. The illumination system includes a second reflectorpositioned relative to the optical device for directing, along the thirddirection, the second light towards the first polarization selectivereflector. The fourth direction is non-parallel to the third direction,and the first polarization is parallel to the second polarization (e.g.,FIG. 14A).

In some embodiments, the second reflector includes a reflective lensstack, and the reflective lens stack includes a second polarizationretarder.

In accordance with some embodiments, an illumination system includes theoptical device, and a spatial light modulator. The second light from thethird direction is the fifth light having the sixth polarization. Insome embodiments, the spatial light modulator receives the portion ofthe second light having the second polarization in the fourth directionfrom the first polarization selective reflector. The first direction iscollinear with the second direction and the fifth direction. The portionof the third light in the sixth direction is transmitted through thefirst polarization selective reflector and is directed by the firstpolarization retarder, as the fourth light having the fourthpolarization, to the first reflector (e.g., FIG. 14D).

In accordance with some embodiments, an illumination system includes theoptical device and a spatial light modulator. The spatial lightmodulator receives the fifth light having the sixth polarization fromthe first polarization retarder. In some embodiments, the seconddirection is collinear with the fifth direction. The third direction iscollinear with the sixth direction. The fourth direction is collinearwith the seventh direction, and the first polarization is parallel tothe second polarization (FIG. 14E).

In some embodiments, the first polarization selective reflector isdisposed on a diagonal of the optical device and a first planecontaining the first polarization selective reflector: (i) intersects,at a first acute angle, with a second plane containing the firstpolarization selective reflector, and (ii) intersects, at a second acuteangle, with a third plane containing the first reflector.

The foregoing description, for purpose of explanation, has beendescribed with reference to specific embodiments. However, theillustrative discussions above are not intended to be exhaustive or tolimit the scope of the claims to the precise forms disclosed. Manymodifications and variations are possible in view of the aboveteachings. The embodiments were chosen in order to best explain theprinciples underlying the claims and their practical applications, tothereby enable others skilled in the art to best use the embodimentswith various modifications as are suited to the particular usescontemplated.

What is claimed is:
 1. An optical device, comprising: a firstpolarization selective reflector positioned in a first orientation sothat the first polarization selective reflector: receives first light ina first direction; redirects a first portion, of the first light, havinga first polarization to a second direction that is non-parallel to thefirst direction; and receives second light in a third direction andtransmit a first portion, of the second light, having a secondpolarization orthogonal to the first polarization; a second polarizationselective reflector positioned in a second orientation non-parallel tothe first orientation, and adjacent to the first polarization selectivereflector so that the second polarization selective reflector: receivesthird light in a fourth direction; redirects a first portion, of thethird light, having the first polarization to a fifth direction that isnon-parallel to the fourth direction; and receives fourth light in asixth direction and transmit a first portion, of the fourth light havingthe second polarization; a light source configured to output the firstlight having the first polarization; and a Fresnel reflector opticallycoupled with the first polarization selective reflector, the Fresnelreflector configured to: receive the first light output by the lightsource; and redirect the first light toward the first polarizationselective reflector.
 2. The optical device of claim 1, wherein: thefirst polarization selective reflector is further configured to transmita second portion, of the first light, having the second polarization;and the second polarization selective reflector is further configured toreceive, and transmit, the second portion, of the first light having thesecond polarization.
 3. The optical device of claim 2, furthercomprising a third reflector configured to receive from the secondpolarization selective reflector the second portion of the first light,and redirect the second portion of the first light back to the secondpolarization selective reflector as the second light.
 4. The opticaldevice of claim 3, further comprising: a waveplate disposed between thethird reflector and the second polarization selective reflector.
 5. Theoptical device of claim 1, wherein: the first polarization selectivereflector is further configured to reflect a second portion, of thesecond light, having the first polarization in a seventh directiondistinct from the third direction; and the second polarization selectivereflector is further configured to reflect a second portion, of thefourth light, having the first polarization, in an eighth directiondistinct from the sixth direction.
 6. The optical device of claim 1,further including a reflective spatial light modulator optically coupledwith the first polarization selective reflector and the secondpolarization selective reflector, the reflective spatial light modulatorconfigured to: receive, on a first region of the reflective spatiallight modulator, the first portion of the first light having the firstpolarization and reflect the first portion of the first light as thesecond light; and receive, on a second region adjacent to the firstregion of the reflective spatial light modulator, the first portion ofthe third light having the first polarization and reflect the firstportion of the third light as the fourth light.
 7. The optical device ofclaim 6, wherein: the reflective spatial light modulator includes areflective surface and a plurality of pixels, a respective pixel in theplurality of pixels having respective modulating elements; andreflecting the first portion of the first light as the second light andreflecting the first portion of the third light as the fourth lightincludes modulating, by the respective modulating elements, polarizationof the first portion of the first light and the first portion of thethird light.
 8. The optical device of claim 6, wherein the reflectivespatial light modulator is a Liquid Crystal on Silicon (LCoS) display.9. The optical device of claim 1, wherein the first polarizationselective reflector in the first orientation and the second polarizationselective reflector in the second orientation define an angle that isapproximately 90 degrees.
 10. The optical device of claim 1, furthercomprising a prism defining a first facet and a second facet, whereinthe first polarization selective reflector is disposed on the firstfacet and the second polarization selective reflector is disposed on thesecond facet.
 11. The optical device of claim 1, further comprising: afirst light source configured to output the first light having the firstpolarization; and a second light source configured to output the thirdlight having the first polarization.
 12. The optical device of claim 11,further comprising: a first Fresnel reflector optically coupled with thefirst polarization selective reflector configured to: receive the firstlight output by the first light source; and redirect the first lighttoward the first polarization selective reflector in the firstdirection; and a second Fresnel reflector optically coupled with thesecond polarization selective reflector configured to: receive the thirdlight output by the second light source; and redirect the third lighttoward the second polarization selective reflector in the fourthdirection.
 13. The optical device of claim 1, wherein the firstpolarization selective reflector in the first orientation and the secondpolarization selective reflector in the second orientation define anangle that is distinct from 90 degrees.
 14. A method, comprising: with alight source, outputting first light having a first polarization; with aFresnel reflector: receiving the first light output by the light source;and redirecting the first light toward a first polarization selectivereflector positioned in a first orientation; with the first polarizationselective reflector: receiving the first light in a first direction;redirecting a first portion, of the first light, having a firstpolarization to a second direction that is non-parallel to the firstdirection; and receiving second light in a third direction, transmit afirst portion, of the second light having a second polarizationorthogonal to the first polarization; and with a second polarizationselective reflector positioned in a second orientation non-parallel tothe first orientation, and adjacent to the first polarization selectivereflector: receiving third light in a fourth direction; redirecting afirst portion, of the third light, having the first polarization to afifth direction that is non-parallel to the fourth direction; andreceiving fourth light in a sixth direction, transmit a first portion,of the fourth light having the second polarization.
 15. The method ofclaim 14, wherein the fourth direction is substantially parallel to thefirst direction.
 16. The method of claim 15, wherein the fifth directionis substantially parallel to the second direction.
 17. The method ofclaim 15, wherein the fifth direction is non-parallel to the seconddirection.
 18. A method of making an optical assembly, the methodcomprising: placing a first polarization selective reflector in a firstorientation; placing a second polarization selective reflector in asecond orientation non-parallel, and adjacent, to the first orientation;and placing a Fresnel reflector, wherein light redirected by the Fresnelreflector is provided toward the first polarization selective reflector.